Previous studies have been done in this laboratory to ascertain the role of intestinal bacteria in hepatic necrosis following excision of the hepatic arterial vasculature in dogs.1 It was demonstrated by culturing portal-vein blood from apparently normal healthy dogs that there was continual seeding of the liver by bacteria that passed from the gastrointestinal tract to the liver by way of the portal vein. It has not been shown in man that bacteria migrate from the gastrointestinal tract into the portal circulation, except in the presence of serious intraperitoneal infections or inflammatory lesions of the gastrointestinal tract. This investigation was undertaken in order to determine whether bacteria enter the portal circulation in the absence of infectious processes. MATERIALS AND METHODS Portal-vein blood obtained from 25 patients at the time of laparotomy was cultured. There was no selection of patients with regard to intraabdominal pathology or type of operation, except