Experimental disseminated intravascular coagulation (DIC) can be induced by 4-h sustained infusion of endotoxin in a dose of 100 mg/kg in rats. The experimental model of DIC in rats was used to study the preventive effect of dipyridamole against DIC. Before the infusion of endotoxin, 0.5, 5.0 or 50.0 mg/kg of dipyridamole was injected intraperitoneally. The preventive effect against DIC was noted in all the parameters, such as fibrinogen and fibrin degradation products, fibrinogen level, prothrombin time, partial thromboplastin time, platelet count, and the number of renal glomeruli with fibrin thrombi, in rats treated with 5.0 or 50.0 mg/kg of dipyridamole. From these results, it was shown that dipyridamole inhibited the aggravation of endotoxin-induced experimental DIC in rats.