The present study was undertaken to assess the possible significance of endotoxaemia and venous stasis of the pancreas in the pathogenesis of acute haemorrhagic pancreatitis. Complete obstruction of the venous drainage of the pancreas in rats induced acute haemorrhagic pancreatic necrosis. Partial venous obstruction caused only oedema and haemorrhage in the interstitium. Systemic endotoxaemia produced slight superficial pancreatic necrosis and fat necrosis, but not oedema or haemorrhage. The administration of endotoxin to the rats with partial obstruction of pancreatic venous outflow caused severe haemorrhagic pancreatic necrosis and a large number of fibrin thrombi in the capillaries and venules in and around the necrotic areas, although the severity of the lesions was less severe when compared with those induced by complete obstruction of pancreatic venous drainage. These findings suggest that acute haemorrhagic pancreatitis can be induced by the coexistence of endotoxaemia and partial venous obstruction of the pancreas. The mechanism may be that the endotoxin-induced capillary and venous fibrin thrombi superimposed upon the venous stasis lead to obstruction of venous drainage of the pancreas severe enough to produce haemorrhagic pancreatic necrosis.