Carnitine plays a significant role in fatty acid utilization and ketone body production. Its availability is especially important during the immediate postnatal period. To determine whether low birth weight infants who cannot be orally fed are at risk of developing carnitine deficiency, we compared the carnitine blood levels and urinary excretion of 12 premature infants (Group A) receiving total parenteral nutrition (TPN) with those of 8 infants of similar gestational age and birth weight (Group B) who received carnitine-containing milk formulas. In Group A, serum levels of total and free carnitine fell after 5 days of carnitine-deficient parenteral nutrition, and urinary excretion was significantly reduced. Serum levels and urinary excretion increased after the onset of oral feedings. The control Group B exhibited no significant changes in carnitine blood levels between the first and fifth days of life, but did show a later increase. Children in Group A had lower carnitine blood levels compared to those in Group B on the fifth day of life. These findings suggest that premature infants are not able to synthesize enough carnitine to maintain blood levels, and that carnitine deficiency can occur following TPN. Further investigation of metabolic consequences secondary to deficient carnitine intake in premature infants is necessary before carnitine supplementation should be considered.