The levels of plasma free carnitine and ketone bodies have been found to fluctuate inversely in fasting individuals without muscle disease. Circulating short-chain acyl-carnitines paralleled beta-hydroxybutyrate levels. A patient with lipid storage myopathy and muscle carnitine deficiency, and his two daughters, developed exaggerated ketogenesis on fasting. The content of total carnitines in the patient's liver was normal, but free carnitine was reduced to 50 percent, and total esterified carnitines were four times greater than the mean value for the controls. The decreased muscle carnitine content in this case may have resulted from chronic hepatic ketogenesis, draining muscle carnitine. Alternatively, decreased muscle carnitine content may have initiated hepatic ketogenesis.