Carnitine metabolism during starvation was studied in adult lean and obese female Zucker rats. Comparisons were made between rats starved for 0, 3, 6 or 9 d. Total plasma carnitine was not affected by obesity or starvation, but free plasma carnitine decreased with starvation. Plasma acid-soluble acylcarnitine was lower in obese than in lean rats, and increased with starvation in both lean and obese rats. Plasma acid-insoluble acylcarnitine was not affected by obesity but increased with starvation. Liver free and acid-soluble acylcarnitine were lower in obese rats than lean rats, and starvation increased liver free carnitine and acid-insoluble acylcarnitine. Free carnitine was lower in muscle from obese rats than from lean rats. In kidney, free carnitine decreased during starvation. Heart carnitine was not affected by obesity or starvation. Urinary free carnitine and acid-soluble acylcarnitine clearance decreased during starvation. These studies indicate that: 1) lean and obese Zucker rats conserve carnitine during starvation; and 2) the decreases in liver carnitine concentration reflect the loss of cellular constituents rather than increases in total hepatic carnitine.