We have studied the effects of warfarin pretreatment on blood coagulation tests, thrombosis and endothelial damage in the rabbit after 2 h of subsequent venous stasis. We found that 3 mg/kg warfarin significantly modified the results of prothrombin time, activated partial thromboplastin time and ProComplex tests. The incidence of thrombosis was not reduced by warfarin, but the weight of the thrombi were inversely related to the effects of the drug on blood coagulation. The endothelial cells showed some degree of damage. In conclusion, warfarin neither prevents endothelial damage nor reduces the incidence of thrombosis after venous stasis, but retards the growth of thrombi.