Ten patients were studied one to seven years following small intestinal bypass for obesity. Liver function tests, normal preoperatively and abnormal early postoperatively, returned to normal 6 to 12 months later. Total serum cholesterol levels decreased by 40% to 50%. Serum protein values stayed within normal limits if the patient was on a high protein diet. Liver biopsies for fatty change preoperatively showed variations from 1% to 75% infiltration. Late postoperative observations in nine patients showed an increase in fatty infiltration in six. In two there was a decrease and in one there was no change. Of these nine patients, in two who developed 80% to 90% infiltration postoperatively, restoration of continuity abolished this histologic evidence of fatty metamorphosis. No evidence of cirrhosis was observed in any patient.