Food intake was measured in 22 obese patients before and after jejunioleostomy for obesity. Most of the weight loss could be accounted for by the observed reduction of caloric intake. Malabsorption was also present as indicated by increased loss of fat in the stools, and decreased absorption of D-xylose and vitamin B12. A dislike for sweet tastes developed after surgery in most patients. Preferences for concentrated solutions of sucrose and glucose were reduced after patients showed a depression of food intake by a 440-calorie preload which had not been detected before surgery. These studies show a decrease in food intake after intestinal bypass surgery and suggest a role for taste or other gastrointestinal factors in regulating food intake.