There are no data concerning long-term utilization of medium-chain triglycerides (MCTs) in parenteral nutrition (PN) in children. Our study included 12 children, aged 1.5-17 yr, on total PN at home, supplying a daily intake of 214 +/- 92 mg/kg nitrogen and 47 +/- 17 kcal/kg nonprotein energy (NPE). NPE included 10-32% long-chain triglycerides (LCTs) (Intralipid 20%). After switching to emulsion containing 50% MCT and 50% LCT (Medialipide) at the same dosage regimen and infusion rate as before, the subjects were monitored at 1, 3, and 6 mo. No signs of clinical intolerance were observed. Among the laboratory parameters evaluated, the only significant (p < 0.05) changes were 1) an increase in apolipoproteins A-I and A-II at 1, 3, and 6 mo and 2) a decrease in gamma-glutamyltransferase (gamma-GT) at 6 mo. There were no changes in the status of essential fatty acids in plasma or in phospholipids (in erythrocyte membranes). Moderate urinary excretion of dicarboxylic acids (adipic, suberic, and sebacic) was evidence of peroxysomal omega-oxidation. The results support the proposal for use of MCT-rich emulsion in long-term PN, given its metabolic advantages relative to LCT.