The present study compared the effects on lipid metabolism of propofol in emulsion (Diprivan) and a fat emulsion (Intralipid) in doses containing the same amount of soya bean oil. Twenty patients received epidural anesthesia for gonarthroscopy and were randomly divided in two groups. Before the start of surgery the patients of group P received a bolus of 2 mg/kg of propofol followed by a one hour infusion of 6 mg/kg/h. In group I, a bolus of 0.2 mg/kg of Intralipid 10% was followed by an infusion of 0.6 ml/kg/h for one hour. These figures represent equivalent amounts of soya bean oil administered. Blood samples were obtained for analysis of serum triglycerides, cholesterol, phospholipids, free fatty acids, aproproteins, and the separated lipoprotein fractions. There were few significant differences between propofol in emulsion and Intralipid in the effects on lipid metabolism. The changes in the measured serum lipid components were mild and rarely lasted longer than 2 h after the end of infusion.