Since ticlopidine specifically inhibits ADP-induced platelet aggregation without affecting prostaglandin metabolism, it seemed interesting to evaluate the effect of aspirin with regard to the antithrombotic efficacy of ticlopidine. Ticlopidine was administered orally to rats alone or in combination with aspirin and the efficacy of the association was determined in several experimental models. A synergistic effect of the ticlopidine/aspirin association was demonstrated with regard to ADP-and collagen-induced platelet aggregation measured ex vivo but also in several experimental thrombosis models including silk thread-induced thrombosis in an arteriovenous shunt, wire coil-induced thrombosis and 111In-labelled platelet deposition on the subendothelium following air drying injury of the rat carotid artery. Similar results were obtained with regard to myointimal proliferation following air-induced injury of the rat carotid artery which occurred as a consequence of vascular injury. The ticlopidine/aspirin combination showed only additive-type effects on bleeding time prolongation induced by tail transection in the rat.