Nineteen newborn infants with necrotizing enterocolitis, proved by autopsy or surgical examination, are presented. In this study the absence of blood in the stools and of pneumatosis intestinalis did not exclude the diagnosis of necrotizing enterocolitis. The role of umbilical arterial and venous catheters and of exchange transfusion in the pathogenesis of the disease was less than has been previously reported. There was no evidence for emboli of thrombosis in the mesenteric vessels. On the other hand, the probable importance of nonocclusive mesenteric arterial insufficiency is supported by several observations, including the high incidence of antecedent hypoxaemic episodes, the time of onset of the subsequent gastrointestinal pathology and the localization of the lesions. An infectious component was demonstrated, but our results do not allow to state precisely the time of its occurrence.