Conventional long chain triglyceride (LCT) was compared with a new emulsion containing 50% medium chain triglyceride (5% MCT/5% LCT) in a randomized cross‐over trial of 10 days duration. Plasma concentrations of albumin, prealbumin, the complement components C3 and C4, and pro‐thrombin times measured daily at 8 am, before lipid infusion, showed no progressive change during the 10 days of the trial, nor in each separate 5‐day period when LCT or MCT/LCT was infused. Aspartate transaminase and alkaline phosphatase activities were similar over the two periods. There was a significant increase (compared with preinfusion levels) in C3 and C4 levels after 5 hr of either lipid infusion. Nitrogen balance was improved, and plasma bilirubin levels were lower on the regimen containing MCT/LCT. (Journal of Parenteral and Enteral Nutrition12:15–19, 1988)