All of the authors with the exception of Frank A. Baglia retract the results of the experiment presented in Figure 3 of Sun M-F, Baglia FA, Ho D, Martincic D, Ware RE, Walsh PN, and Gailani D. Defective binding of factor XI-N248 to activated human platelets. Blood. 2001;98:125–129, because recent experiments conducted by Dipali Sinha, Sergei Shikov, Wenman Wu, and Syed Ahmad in the laboratory of Peter N. Walsh fail to confirm the conclusion that activated platelets promote the activation of factor XI by thrombin. All of the other results reported in this paper are valid. A detailed explanation of the chronology of events leading to this retraction and the retraction of 2 papers (Baglia FA, Walsh PN. Prothrombin is a cofactor for the binding of factor XI to the platelet surface and for platelet-mediated factor XI activation by thrombin. Biochemistry. 1998;37:2271-2281; Baglia FA, Walsh PN. Thrombin-mediated feedback activation of factor XI on the activated platelet surface is preferred over contact activation by factor XIIa or factor XIa. J Biol Chem. 2000;275:20514-20519) have been published in the journal Biochemistry (bi-2007-01501k, accepted July 27, 2007). We apologize to the readers, reviewers, and editors of Blood for publishing these erroneous data.

Mao-Fu Sun, David Ho, Danko Martincic, Russell E. Ware, Peter N. Walsh, and David Gailani, authors