A randomized, double-blind multicenter trial-the Clopidogrel and Aspirin: Determination of the Effects on Thrombogenicity (CADET) trial-was carried out to compare the effects of clopidogrel vs. aspirin on thrombotic variables and C-reactive protein (CRP), over a 6-month period of treatment, in patients with an acute myocardial infarction within the previous 3-7 days, who were not scheduled for major surgery including coronary artery bypass grafting. Patients (n = 184) were randomly allocated to aspirin (75 mg day(-1)) or clopidogrel (75 mg day(-1)). Blood samples were taken at baseline and then at clinic visits at 1, 3 and 6 months. By 1 month, clottable and immunonephelometric fibrinogen, D-dimer, von Willebrand factor, factor VIII and CRP were significantly (P < 0.05) reduced from baseline values in both treatment groups; as well as tissue plasminogen activator antigen in the aspirin group only. At 6 months, there were no differences between treatment groups (P > 0.05) for any of the variables, whether or not potential confounding variables were adjusted for. Similarly, there were no differences between treatments in the difference between baseline and final values for any of the variables. Aspirin and clopidogrel were thus found to have similar effects on thrombotic variables and CRP in this patient population.