Primary and secondary carnitine deficiency syndromes are characterized by myopathy, encephalopathy and hepatopathy. We measured plasma levels of free and esterified carnitine in 20 patients from our neurological intensive care unit who required intravenous or tube feeding. After 2-3 weeks 19 patients showed a 30%-60% decrease in the levels of serum free and total carnitine. As soon as oral feeding was recommenced, carnitine levels quickly returned to normal. These data suggest the need for new carnitine-enriched feeding fluids, which are presently under investigation.