X0303 4 2010-02-24 0001278021 MARKETAXESS HOLDINGS INC MKTX 0001296468 Themelis Nicholas C/O MARKETAXESS HOLDINGS INC. 140 BROADWAY, 42ND FLOOR NEW YORK NY 10005 0 1 0 0 Chief Information Officer Common Stock, par value $0.003 per share 2010-02-24 4 S 0 3838 15.3851 D 156057 D Common Stock, par value $0.003 per share 2010-02-25 4 S 0 11162 15.0949 D 144895 D The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $15.37 to $15.41, inclusive. The reporting person undertakes to provide to MarketAxess Holdings Inc., any security holder of MarketAxess Holdings Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnotes (1) and (2) to this Form 4. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $15.02 to $15.23, inclusive. /s/ Ori Solomon, as Attorney-in-Fact for Nicholas Themelis 2010-02-26