This experiment was undertaken to clarify the effect of fat emulsion administered immediately after an operation. Total parenteral nutrition (TPN) was supplied to rats after partial resection of the small intestine. Animals were divided in two groups according to the TPN regimen: TPN without fat (TPN-G) and TPN with 30% of the non-protein calories provided by fat emulsion (TPN-F). TPN-F and TPN-G showed similar effects on body weight and nitrogen balance. The fat emulsion did not cause deleterious effects. Fat content of the liver was increased at 3 POD in both groups. The increase was attributable to triglycerides. Liver and muscle glycogen rose at 3 POD and returned to preoperative values at 5 POD. The results show that fat emulsion providing 30% of the non-protein calories is utilized as well as glucose in the immediate postoperative period.