A number of hemostatic parameters reflecting the activation of coagulation and fibrinolysis were investigated in a prospective study of 24 patients undergoing cardiopulmonary bypass (CPB) during heart surgery. The patients were randomized to a group in which either a roller (group 1) or a centrifugal pump (group 2) was used. Blood samples were taken preoperatively, at the onset of and every 20 min during CPB, after the administration of protamine, and 4, 20, 44, and 68 h postoperatively. The groups did not differ significantly in hematocrit, fibrinogen, factor XIII, and antithrombin III. Significant differences in favor of group 2 during and after CPB were found in prothrombin fragment F1 + 2, plasmin-antiplasmin complex (PAP), thrombin-antithrombin complex (TAT), and D-dimer (F1 + 2 P < 0.01 after 80-min CPB, PAP P < 0.005 after 40-min CPB, TAT and D-dimer P < 0.05 after 100-min CPB, D-dimer and PAP P < 0.05 after protamine administration, TAT and F1 + 2 4 h after CPB). These findings indicate the activation of fibrinolysis preceding thrombin generation during cardiopulmonary bypass. In addition, we conclude that centrifugal blood pumping is beneficial in avoiding excessive activation of both coagulation and fibrinolysis.