The effect of carnitine administration on neonatal lipid metabolism was studied during endovenous loading with Intralipid (1 g/kg body weight over a 4-hour period). During a 6-hour period the plasma level of triglycerides, glycerol, free fatty acids (FFA), beta-hydroxybutyrate (beta-OHB), and acetoacetate were monitored in a group of newborns infused with carnitine and compared with a control group infused only with Intralipid. Carnitine administration caused an increased plasma concentration of ketone bodies, probably consequent to an increased rate of FFA mitochondrial beta-oxidation. An increased plasma level of glycerol and FFA was also observed, whereas the triglyceride plasma levels were not different between the two groups. Carnitine administration in the neonatal period seems to act by increasing ketogenesis and lipolysis.