Experimental disseminated intravascular coagulation (DIC) can be induced by a 4-hr sustained infusion of endotoxin at a dose of 100 mg/kg in rats. This experimental model of DIC in rats was used to study the effects of defibrinogenation with batroxobin against DIC. One hour before the infusion of endotoxin, 200 batroxobin unit (BU)/kg of batroxobin was injected intraperitoneally. Immediately after the injection, fibrinogen level markedly decreased and fibrinogen and fibrin degradation products increased. Prothrombin time and partial thromboplastin time were also prolonged. Blood counts, platelet counts and hematocrit level only showed a slight decrease after the injection. The preventive effect against DIC was noted by the partial inhibition of the fall in the platelet counts and lessened number of renal glomeruli with fibrin thrombi, in the rats treated with 200 BU/kg of batroxobin 1 hr before the infusion of endotoxin (100 mg/kg/4 hr). From these results, it was shown that fibrinogen metabolism plays an important role in the DIC state.