Six patients near term were given an intravenous infusion of a fat emulsion (Intralipid) a few hours before normal delivery or Caesarean section. Six other non-infused patients were studied as controls. Maternal venous and umbilical venous and arterial blood samples were taken at delivery and analyzed for individual fatty acid concentrations in triglyceride, free fatty acid (FFA) and phospholipid fractions. The emulsion, being rich in oleic and linoleic acids, affected the composition of the maternal triglycerides. The fetal lipids were also altered and the infusions resulted in large positive umbilical venous-arterial (v-a) differences in FFA and triglyceride fatty acid concentrations, but this was not the case for phospholipid concentrations. The fatty acids with the largest v-a differences were those prominent in the emulsion.