To determine the serum free carnitine concentration in normally nourished children and in children with kwashiorkor and to relate the carnitine concentration to the ability to oxidise exogenous long chain fatty acids in the body.A cross-sectional comparative study of two age-matched groups.Forty seven children with kwashiorkor and 47 age-matched normally nourished children.Fasting blood samples were enzymatically analysed for free carnitine levels. 13C labelled hiolein was administered orally and the recovery of 13C from the breath air was monitored after administration of the feed. The cumulative per cent dose (CUMPD) recovery of 13C 16 hours after the ingestion of labelled hiolein was determined.Normal children had significantly higher free carnitine concentrations (mean = 60.7 mumol/l; 95% confidence interval of the mean = 42.7-77.8) than the kwashiorkor children (mean = 16.5 mumol/l; 95% confidence interval of the mean = 11.3-19.8)(p < 0.001). There was no correlation between serum free carnitine concentration and serum albumin in kwashiorkor subjects, but there was a significant correlation between serum free carnitine concentration and the degree of weight loss as indicated by the weight: weight for age and sex ratio. The greater the weight loss, the lower the serum carnitine concentration amongst the kwashiorkor children (r = 0.46; p < 0.01). There was a linear relationship between serum free carnitine and hiolein oxidation (r = 0.89; p < 0.001).There is carnitine deficiency in kwashiorkor, and that the impaired lipid oxidation in kwashiorkor is related to this deficiency.