The effects of ticlopidine and aspirin on endotoxin-induced experimental disseminated intravascular coagulation (DIC) were studied in rats. Experimental DIC was induced by a 4 hr sustained infusion of endotoxin at a dose of 100 mg/kg. The rats were intraperitoneally injected with ticlopidine at 2.0, 20.0, 50.0, 100.0 or 200.0 mg/kg, or aspirin at 0.03, 0.3, 3.0 or 30.0 mg/kg, followed by the continuous infusion of 100 mg/kg/4 hr of endotoxin. A preventive effect against DIC was noted in all the parameters, such as fibrinogen and fibrin degradation products (FDP), fibrinogen level, prothrombin time, partial thromboplastin time (PTT), platelet count and the number of renal glomeruli with fibrin thrombi, in the rats treated with 20.0, 50.0, 100.0 or 200.0 mg/kg of ticlopidine. Although a preventive effect was also noted in FDP, PTT, platelet count and the number of glomeruli with thrombi in rats treated with 0.03 or 0.3 mg/kg of aspirin, this agent was less effective than ticlopidine.