This study examines the evolution of the thrombotic activity in patients with myocardial infarction (MI) treated with aspirin (200 mg/day) for 2 years after MI. Plasma samples of 10 patients were collected at 7, 30, 60, 90, 120, 150, 180, 360 and 720 days. In all the samples we measured fibrinogen (Fg), high molecular weight Fg (HMW-Fg), fibrinopeptide A (FPA), prothrombin fragment 1+2 (F1+2), beta-thromboglobulin (beta-TG), von Willebrand factor (vWF), tissue factor (TF) and TF pathway inhibitor (TFPI). The plasma Fg, HMW-Fg, FPA, F1+2, beta-TG and vWF levels were significantly elevated in the patients at the beginning of the study as compared to the normal group. The 95% confidence intervals were Fg 277-333 mg/dl, HMW-Fg 200-244 mg/dl, FPA 5.3-16.5 ng/ml, F1+2 1.4-1.8 nmol/l, beta-TG 110-118 IU/ml and vWF 139-195%. At thirty days Fg and HMW-Fg returned to normal levels, whereas the increase in FPA and F1+2 levels persisted throughout the study. At 120 and 150 days, respectively, beta-TG and vWF returned to normal levels. The increase in thrombin generation and activity pointed to a persistent hypercoagulable state 2 years after MI. Plasma levels of TF and TFPI showed no statistically significant variations with respect to the normal values over the 2-year period studied. In conclusion, these results suggest a persistent generation and activity of thrombin and cellular activation in these patients after MI.