Lipid emulsions containing both long- and medium-chain triglycerides (LCT/MCT) have been used in total parenteral nutrition (TPN) regimens and seem to have certain advantages for seriously ill patients. The aim of the present study was to investigate the effect of lipid emulsions containing 100% LCT or 50% LCT/50% MCT on tumor necrosis factor (TNF) production by human mononuclear cells.This was a prospective study, in which 20 malnourished patients were randomly allocated to receive either 100% LCT or 50% LCT/50% MCT for>30 days. We measured TNF synthesis before initiation of TPN, as well as at 15 and 30 days during TPN.Departments of Medicine and Surgery, Patras University Medical School, Patras, Greece.Members of the staff of the Departments of Medicine and Surgery, Patras University Medical School.We found that TNF production was significantly (p<0.01) elevated at 30 days in the LCT group, while no significant differences were detected in the LCT/MCT group.It is concluded that long-term TPN formulas, where LCT have been partially replaced by MCT, do not change TNF synthesis by peripheral blood mononuclear cells, and this may be beneficial in seriously ill, cachectic patients.