UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 1)* MARKETAXESS HOLDINGS INC. -------------------------------------------------------------------------------- (Name of Issuer) COMMON STOCK, PAR VALUE $0.003 PER SHARE -------------------------------------------------------------------------------- (Title of Class of Securities) 57060D 10 8 -------------------------------------------------------------------------------- (CUSIP Number) DECEMBER 31, 2005 -------------------------------------------------------------------------------- (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule pursuant to which this Schedule is filed: [ ] Rule 13d-1(b) [ ] Rule 13d-1(c) [x] Rule 13d-1(d) *The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which could alter the disclosures provided in a prior cover page. The information required in the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes). Page 1 of 16 Pages 13G CUSIP No. 57060D 10 8 Page 2 of 16 Pages -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON J.P. Morgan Partners (23A SBIC), L.P. (f/k/a J.P. Morgan Partners (23A SBIC), LLC) 13-3986302 -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) [ ] (b) [ ] -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 CITIZENSHIP OR PLACE OF ORGANIZATION Delaware -------------------------------------------------------------------------------- 5 SOLE VOTING POWER NUMBER OF 800,000 shares of Common Stock SHARES ------------------------------------------------------------------- BENEFICIALLY 6 SHARED VOTING POWER OWNED BY EACH 912,589 shares of Common Stock (See Item 4(c)) REPORTING ------------------------------------------------------------------- PERSON 7 SOLE DISPOSITIVE POWER WITH 800,000 shares of Common Stock -------------------------------------------------------------------- 8 SHARED DISPOSITIVE POWER 912,589 shares of Common Stock (See Item 4(c)) -------------------------------------------------------------------------------- 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,712,589 shares of Common Stock (See Item 4(a)) -------------------------------------------------------------------------------- 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES* -------------------------------------------------------------------------------- PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 11 Approximately 9.99% as of the date of this Statement (based on 24,238,460 shares of Common Stock reported to be issued and outstanding as of November 4, 2005 on the Issuer's Quarterly Report on Form 10-Q filed on November 9, 2005). (See Item 4(b)) -------------------------------------------------------------------------------- TYPE OF REPORTING PERSON* 12 PN - Partnership -------------------------------------------------------------------------------- Page 2 of 16 Pages 13G CUSIP No. 57060D 10 8 Page 3 of 16 Pages -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON LabMorgan Corporation 13-4184941 -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) [ ] (b) [ ] -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 CITIZENSHIP OR PLACE OF ORGANIZATION Delaware -------------------------------------------------------------------------------- 5 SOLE VOTING POWER NUMBER OF 800,000 shares of Common Stock SHARES ------------------------------------------------------------------- BENEFICIALLY 6 SHARED VOTING POWER OWNED BY EACH 912,589 shares of Common Stock (See Item 4(c)) REPORTING ------------------------------------------------------------------- PERSON 7 SOLE DISPOSITIVE POWER WITH 800,000 shares of Common Stock -------------------------------------------------------------------- 8 SHARED DISPOSITIVE POWER 912,589 shares of Common Stock (See Item 4(c)) -------------------------------------------------------------------------------- 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,712,589 shares of Common Stock (See Item 4(a)) -------------------------------------------------------------------------------- 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES* -------------------------------------------------------------------------------- PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 11 Approximately 9.99% as of the date of this Statement (based on 24,238,460 shares of Common Stock reported to be issued and outstanding as of November 4, 2005 on the Issuer's Quarterly Report on Form 10-Q filed on November 9, 2005). (See Item 4(b)) -------------------------------------------------------------------------------- TYPE OF REPORTING PERSON* 12 CO - Corporation -------------------------------------------------------------------------------- Page 3 of 16 Pages ITEM 1. (a) Name of Issuer MarketAxess Holdings Inc. (b) Address of Issuer's Principal Executive Offices: 140 Broadway, 42nd Floor New York, NY 10005 ITEM 2. (a) Name of Persons Filing: J.P. Morgan Partners (23A SBIC), L.P. ("JPMP (23A SBIC)") LabMorgan Corporation ("LabMorgan") Supplemental information relating to the ownership and control of the persons filing this Statement is included in Exhibit 2(a) attached hereto. (b) Address of Principal Business Office: 1221 Avenue of the Americas New York, NY 10020 (c) Citizenship: Delaware (d) Title of Class of Securities: Common Stock, par value $0.003 per share (e) CUSIP Number: 57060D 10 8 ITEM 3. IF THIS STATEMENT IS FILED PURSUANT TO RULE 13D-1(B), OR 13D-2(B), CHECK WHETHER THE PERSON FILING IS A: (a) |_| Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o). (b) |_| Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c). (c) |_| Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c). Page 4 of 16 Pages (d) |_| Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8). (e) |_| An investment adviser in accordance with ss.240.13d-1(b)(1)(ii)(E); (f) |_| An employee benefit plan or endowment fund in accordance with ss.240.13d-1(b)(1)(ii)(F); (g) |_| A parent holding company or control person in accordance with ss. 240.13d-1(b)(1)(ii)(G); (h) |_| A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813); (i) |_| A church plan that is excluded from the definition of an investmentcompany under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3); (j) |_| Group, in accordance with ss.240.13d-1(b)(1)(ii)(J). If this statement is filed pursuant to Rule 13d-1(c), check this box |_| ITEM 4. OWNERSHIP (a) Amount Beneficially Owned JPMP (23A SBIC): 1,712,589 shares of Common Stock (includes 912,589 shares of Common Stock issuable to JPMP (23A SBIC) upon conversion of shares of nonvoting common stock, par value $0.003 per share, of the Issuer ("Nonvoting Common Stock") held by JPMP (23A SBIC)). This amount excludes (i) 800,000 shares of Common Stock held by LabMorgan and included below, and (ii) the remaining 312,728 shares of Nonvoting Common Stock held by JPMP (23A SBIC) because the terms of the Nonvoting Common Stock contain a limitation on acquiring shares of Common Stock if the conversion would result in the holder beneficially owning more than 9.99% of the outstanding shares of Common Stock. In total, 800,000 shares of Common Stock and 1,225,317 shares of Nonvoting Common Stock are owned by JPMP (23A SBIC). LabMorgan: 1,712,589 shares of Common Stock (includes 912,589 shares of Common Stock issuable to LabMorgan pursuant to any combination of the exercise of a warrant (the "Warrant") or the conversion of shares of Nonvoting Common Stock held by LabMorgan). This amount excludes (i) 800,000 shares of Common Stock held by JPMP and included above, and (ii) an aggregate of 1,681,381 shares from any combination of the remaining portion of the Nonvoting Common Stock Page 5 of 16 Pages and the remaining portion of the Warrant, because the terms of the Nonvoting Common Stock and the Warrant contain a limitation on acquiring shares of Common Stock if the conversion or exercise would result in the holder beneficially owning more than 9.99% of the outstanding shares of Common Stock. In total, 800,000 shares of Common Stock, 1,360,337 shares of Nonvoting Common Stock and a Warrant to purchase 1,233,633 shares of Common Stock are owned by LabMorgan. (b) Percent of Class Approximately 9.99% as of the date of this Statement (based on 24,238,460 shares of Common Stock issued and outstanding as of November 4, 2005 on the Issuer's Quarterly Report on Form 10-Q filed on November 9, 2005). (c) Number of shares as to which the person has: (i) Sole power to vote or direct the vote: JPMP (23A SBIC): 800,000 shares of Common Stock LabMorgan: 800,000 shares of Common Stock (ii) Shared power to vote or direct the vote: JPMP (23A SBIC): 912,589 shares of Common Stock LabMorgan: 912,589 shares of Common Stock JPMP (23A SBIC) and LabMorgan share the power to vote or direct the vote of these shares of Common Stock because they each have the right to acquire a maximum of 912,589 shares of Common Stock pursuant to any combination of the conversion of shares of Nonvoting Common Stock held by each of them or the exercise of the Warrant held by LabMorgan. To the extent that one of JPMP (23A SBIC) or LabMorgan so acquires such shares of Common Stock, the other is precluded from acquiring such shares of Common Stock because the terms of the Nonvoting Common Stock and the Warrant contain a limitation on acquiring shares of Common Stock if the conversion or exercise would result in the holder beneficially owning more than 9.99% of the outstanding shares of Common Stock. (iii) Sole power to dispose or to direct the disposition of: JPMP (23A SBIC): 800,000 shares of Common Stock LabMorgan: 800,000 shares of Common Stock (iv) Shared power to dispose or to direct the disposition of: JPMP (23A SBIC): 912,589 shares of Common Stock Page 6 of 16 Pages LabMorgan: 912,589 shares of Common Stock JPMP (23A SBIC) and LabMorgan share the power to dispose or to direct the disposition of these shares of Common Stock because they each have the right to acquire a maximum of 912,589 shares of Common Stock pursuant to any combination of the conversion of shares of Nonvoting Common Stock held by each of them or the exercise of the Warrant held by LabMorgan. To the extent that one of JPMP (23A SBIC) or LabMorgan so acquires such shares of Common Stock, the other is precluded from acquiring such shares of Common Stock because the terms of the Nonvoting Common Stock and the Warrant contain a limitation on acquiring shares of Common Stock if the conversion or exercise would result in the holder beneficially owning more than 9.99% of the outstanding shares of Common Stock ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS Inapplicable ITEM 6. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON Inapplicable Item 7. Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company Inapplicable ITEM 8. IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP See the Joint Filing Agreement Attached hereto as Exhibit 8. ITEM 9. NOTICE OF DISSOLUTION OF THE GROUP Inapplicable ITEM 10. CERTIFICATION Inapplicable Page 7 of 16 SIGNATURE After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct. Dated this 13th day of February, 2006 J.P. MORGAN PARTNERS (23A SBIC), L.P. By: J.P. Morgan Partners (23A SBIC Manager), Inc., its General Partner By: /s/Jeffrey C. Walker ---------------------------------------- Name: Jeffrey C. Walker Title: President LABMORGAN CORPORATION By: /s/Jeffrey C. Walker ---------------------------------------- Name: Jeffrey C. Walker Title: President Page 8 of 16 Pages EXHIBIT 2(a) This statement is being filed by J.P. Morgan Partners (23A SBIC), L.P., a Delaware limited partnership (hereinafter referred to as "JPMP (23A SBIC)"), and LabMorgan Corporation, a Delaware corporation (hereinafter referred to as "LabMorgan"). The principal business address of JPMP (23A SBIC) and LabMorgan is 1221 Avenue of the Americas, New York, NY 10020. JPMP (23A SBIC) is engaged in the venture capital and leveraged buyout business. The general partner of JPMP (23A SBIC) is J.P. Morgan Partners (23A SBIC Manager), Inc., a Delaware corporation (hereinafter referred to as "JPMP (23A Manager)"), whose principal business office is located at the same address as JPMP (23A SBIC) and is also indirectly (through JPMP (23A SBIC)) engaged in the venture capital and leveraged buyout business. Set forth in Schedule A hereto and incorporated herein by reference are the names, business addresses, principal occupations and employment of each executive officer and director of JPMP (23A Manager). As general partner of JPMP (23A SBIC), JPMP 23A Manager may be deemed to beneficially own the shares held by JPMP (23A SBIC). JPMP (23A Manager) is a wholly owned subsidiary of JPMorgan Chase Bank, National Association, a National Banking Association (hereinafter referred to as "JPM Chase Bank") which is engaged in the commercial banking business with its principal office located at 270 Park Avenue, New York, New York 10017. Set forth in Schedule B hereto and incorporated herein by reference are the names, business addresses, principal occupations and employments of each executive officer and director of JPM Chase Bank. JPM Chase Bank is a wholly owned subsidiary of JPMorgan Chase & Co., a Delaware corporation (hereinafter referred to as "JPMorgan Chase") which is engaged (primarily through subsidiaries) in the commercial banking business with its principal office located at 270 Park Avenue, New York, New York 10017. Set forth in Schedule C hereto and incorporated herein by reference are the names, business addresses, principal occupations and employments of each executive officer and director of JPMorgan Chase. LabMorgan is engaged in the venture capital and leveraged buyout business. Set forth in Schedule D hereto and incorporated herein by reference are the names, business addresses, principal occupations and employment of each executive officer and director of LabMorgan. LabMorgan is a wholly owned subsidiary of JPMorgan Chase, which is described above. Page 9 of 16 Pages SCHEDULE A J.P. MORGAN PARTNERS (SBIC 23A MANAGER), INC. EXECUTIVE OFFICERS(1) Jeffrey C. Walker* President Arnold L. Chavkin* Chief Investment Officer Srinivas Akkaraju* Managing Director Christopher Albinson* Managing Director Dr. Dana Beth Ardi* Managing Director Christopher C. Behrens* Managing Director John Breckenridge* Managing Director Julie Casella-Esposito* Managing Director Rodney A. Ferguson* Managing Director Michael Hannon* Managing Director Mathew Lori* Managing Director Jonathan R. Lynch* Managing Director Stephen McKenna* Managing Director Sunil Mishra* Managing Director Stephen P. Murray* Managing Director Kevin O'Brien* Managing Director Timothy Purcell* Managing Director John Reardon* Managing Director Faith Rosenfeld* Managing Director Shahan D. Soghikian* Managing Director William Stuek* Managing Director Lauren Tyler* Managing Director Timothy Walsh* Managing Director Richard D. Waters, Jr.* Managing Director Damion E. Wicker, M.D.* Managing Director SOLE DIRECTOR (1) Jeffrey C. Walker* ---------------- (1) Each of whom is a United States citizen. * Principal occupation is employee and/or officer of J.P. Morgan Partners, LLC. Business address is c/o J.P. Morgan Partners, LLC, 1221 Avenue of the Americas, New York, New York 10020. Page 10 of 16 Pages SCHEDULE B JPMORGAN CHASE BANK, NATIONAL ASSOCIATION EXECUTIVE OFFICERS(1) William B. Harrison, Jr. Chairman of the Board James Dimon President and Chief Executive Officer Austin A. Adams Chief Information Officer Frank Bisignano Chief Administrative Officer Steven D. Black Co-CEO, Investment Bank John F. Bradley Director Human Resources Michael J. Cavanagh Chief Financial Officer Ina R. Drew Chief Investment Officer Joan Guggenheimer Co-General Counsel Samuel Todd Maclin Head, Commercial Banking Jay Mandelbaum Head, Strategy William H. McDavid Co-General Counsel Heidi Miller EVP, Treasury & Securities Services Charles W. Scharf Head, Retail Financial Services Richard J. Srednicki EVP & CEO, Card Services James E. Staley Head, Asset & Wealth Management Don M. Wilson III Chief Risk Officer William T. Winters MD & Co-CEO, Investment Bank (1) Each of whom is a United States citizen whose principal occupation is employee or officer of J.P. Morgan Chase & Co. Business address is c/o J.P. Morgan Chase & Co., 270 Park Avenue, New York, New York 10017. Page 11 of 16 Pages DIRECTORS(1) NAME PRINCIPAL OCCUPATION OR EMPLOYMENT ---- ---------------------------------- William B. Harrison, Jr. Chairman of the Board James Dimon President and Chief Executive Officer Michael J. Cavanagh Chief Financial Officer Charles W. Scharf Head, Retail Financial Services Don M. Wilson III Chief Risk Officer ----------------- (1) Each of whom is a United States citizen and has a business address of c/o J.P. Morgan Chase & Co., 270 Park Avenue, New York, New York 10017. Page 12 of 16 Pages SCHEDULE C JPMORGAN CHASE & CO. EXECUTIVE OFFICERS(1) William B. Harrison, Jr. Chairman of the Board James Dimon President and Chief Executive Officer Austin A. Adams Chief Information Officer Frank Bisignano Chief Administrative Officer Steven D. Black Co-CEO, Investment Bank John F. Bradley Director Human Resources Michael J. Cavanagh Chief Financial Officer Ina R. Drew Chief Investment Officer Joan Guggenheimer Co-General Counsel Samuel Todd Maclin Head, Commercial Banking Jay Mandelbaum Head, Strategy William H. McDavid Co-General Counsel Heidi Miller EVP, Treasury & Securities Services Charles W. Scharf Head, Retail Financial Services Richard J. Srednicki EVP & CEO, Card Services James E. Staley Head, Asset & Wealth Management Don M. Wilson III Chief Risk Officer William T. Winters MD & Co-CEO, Investment Bank (1) Each of whom is a United States citizen whose principal occupation is employee or officer of J.P. Morgan Chase & Co. Business address is c/o J.P. Morgan Chase & Co., 270 Park Avenue, New York, New York 10017. Page 13 of 16 Pages DIRECTORS(1) NAME PRINCIPAL OCCUPATION OR EMPLOYMENT -------------------------------------------------------------------------------- Hans W. Becherer Retired Chairman of the Board and Chief Executive Officer Deere & Company -------------------------------------------------------------------------------- John H. Biggs Former Chairman and CEO TIAA - CREF -------------------------------------------------------------------------------- Lawrence A. Bossidy Retired Chairman of the Board Honeywell International Inc. -------------------------------------------------------------------------------- Stephen B. Burke President Comcast Cable Communications, Inc. -------------------------------------------------------------------------------- James S. Crown President Henry Crown and Company -------------------------------------------------------------------------------- James Dimon President and Chief Executive Officer JPMorgan Chase & Co. -------------------------------------------------------------------------------- Ellen V. Futter President and Trustee American Museum of Natural History -------------------------------------------------------------------------------- William H. Gray, III Retired President and Chief Executive Officer The College Fund/UNCF -------------------------------------------------------------------------------- William B. Harrison, Jr. Chairman of the Board JPMorgan Chase & Co. -------------------------------------------------------------------------------- Laban P. Jackson, Jr. Chairman and Chief Executive Officer Clear Creek Properties, Inc. -------------------------------------------------------------------------------- John W. Kessler Owner John W. Kessler Company -------------------------------------------------------------------------------- Robert I. Lipp Senior Advisor JPMorgan Chase & Co. -------------------------------------------------------------------------------- Richard A. Monoogian Chairman and Chief Executive Officer Masco Corporation -------------------------------------------------------------------------------- David C. Novak Chairman and Chief Executive Officer Yum! Brands, Inc. -------------------------------------------------------------------------------- Lee R. Raymond Chairman of the Board and Chief Executive Officer Exxon Mobil Corporation -------------------------------------------------------------------------------- William C. Weldon Chairman and Chief Executive Officer Johnson & Johnson -------------------------------------------------------------------------------- (1) Each of whom is a United States citizen and has a business address of c/o JPMorgan Chase & Co, 270 Park Avenue, New York, New York 10017. Page 14 of 16 Pages SCHEDULE D LABMORGAN CORPORATION EXECUTIVE OFFICERS(1) Jeffrey C. Walker* President Arnold L. Chavkin* Chief Investment Officer Srinivas Akkaraju* Managing Director Christopher Albinson* Managing Director Dr. Dana Beth Ardi* Managing Director Christopher C. Behrens* Managing Director John Breckenridge* Managing Director Carty Chock* Managing Director Julie Casella-Esposito* Managing Director Rodney A. Ferguson* Managing Director Michael Hannon* Managing Director Tom Horn* Managing Director Mathew Lori* Managing Director Jonathan R. Lynch* Managing Director Stephen McKenna* Managing Director Sunil Mishra* Managing Director Stephen P. Murray* Managing Director Kevin O'Brien* Managing Director Timothy Purcell* Managing Director John Reardon* Managing Director Faith Rosenfeld* Managing Director Shahan D. Soghikian* Managing Director William Stuek* Managing Director Lauren Tyler* Managing Director Timothy Walsh* Managing Director Richard D. Waters, Jr.* Managing Director Damion E. Wicker, M.D.* Managing Director John Wilmot* Managing Director SOLE DIRECTOR(1) Jeffrey C. Walker* ----------------- (1) Each of whom is a United States citizen. * Principal occupation is employee and/or officer of J.P. Morgan Partners, LLC. Business address is c/o J.P. Morgan Partners, LLC, 1221 Avenue of the Americas, New York, New York 10020. Page 15 of 16 Pages EXHIBIT 8 JOINT FILING AGREEMENT The undersigned hereby agree that they are filing this statement jointly pursuant to Rule 13d-1(k)(1). Each of them is responsible for the timely filing of such Schedule 13G and any amendments thereto, and for the completeness and accuracy of the information concerning such person contained therein; but none of them is responsible for the completeness or accuracy of the information concerning the other persons making the filing, unless such person knows or has reason to believe that such information is inaccurate. In accordance with Rule 13d-1(k)(1) promulgated under the Securities and Exchange Act of 1934, as amended, the undersigned hereby agree to the joint filing with each other on behalf of each of them of to such a statement on Schedule 13G with respect to the common stock of MarketAxess Holdings Inc. beneficially owned by each of them. This Joint Filing Agreement shall be included as an exhibit to such Schedule 13G. IN WITNESS WHEREOF, the undersigned hereby executed this agreement on February 13th, 2006. J.P. MORGAN PARTNERS (23A SBIC), L.P. By: J.P. Morgan Partners (23A SBIC Manager), Inc., its General Partner By: /s/Jeffrey C. Walker -------------------- Name: Jeffrey C. Walker Title: President LABMORGAN CORPORATION By: /s/Jeffrey C. Walker -------------------- Name: Jeffrey C. Walker Title: President Page 16 of 16 Pages