Material and Methods: 196 patients undergoing resection for pancreatic and gastric cancer were randomized in double-blind manner to receive early postoperative enteral nutrition with immunostimulating diet (IMEN group: formula supplemented with arginine, glutamine, omega-3 fatty acids) or oligopeptic control (SEN group) between June 2004 and September 2007. Enteral nutrition was started 6 hours after surgery and continued for 7 days, up to target volume of 100 ml/h. All malnourished patients requiring preoperative nutritional therapy were excluded for the study and treated preoperatively. Outcome measures were: number and type of complications, length of hospital stay, mortality, treatment tolerance, liver and kidney function.