The use of lipid emulsions for TPN remains controversial. Although experimental studies show that medium chain triglycerides (MCT) are beneficial over long chain triglycerides (LCT) clinical studies are contradictory. With the aim to study the clearance of two lipid emulsions a prospective study was designed. 21 patients, submitted to resective surgery because of upper gastrointestinal tract malignancy were randomized in three groups. In group I (without lipids): all caloric intake was supplied by hypertonic glucose solution. In group II (LCT group) 55% of caloric intake was supplied by glucose and 45% by a LCT 20% emulsion (Intralip[id 20%, Kabi-Pharmacia). In group III (MCT group) 55% of caloric intake was supplied by hypertonic glucose solution and 45% by a physical mixture of LCT and MCT at 20% concentration (Lipofundina MCT, B. Braun). Our results show that in postoperative period of major abdominal surgery both lipid emulsions are cleared of in a similar way. When these emulsions are administered during 12 hours per day plasmatic triglycerides are completely cleared before to start the next-day infusion of lipid emulsion. Differences in total cholesterol were not found between groups. Nevertheless LDL-cholesterol rose significatively between first and tenth postoperative day in LCT group.