In experimental animals the enhancement of hepatic fatty acid oxidation and ketogenic capacity is accompanied by a rise in the concentration of liver carnitine. Massive obesity is characterized by enhanced fatty acid turnover, insulin resistance, and often a fatty liver. Carnitine concentrations were determined in liver, abdominal muscle tissue, and blood in morbidly obese women. The liver and muscle carnitine concentrations were significantly higher in the obese subjects than in the lean control subjects. These findings suggest an increase of the whole-body carnitine pool. In the obese subjects there was also a significant positive correlation between liver and muscle carnitine concentrations. In the majority of the obese subjects fatty changes could be demonstrated in the liver. The plasma insulin concentration tended to be positively correlated with the degree of fat infiltration and negatively correlated with the liver carnitine content. It is concluded that the liver carnitine content is significantly increased in obese women, which agrees with the finding in experimental animals.