[en] The syntheses of L-carnitine, O-acetyl CoA, and O-acetyl-L-carnitine labelled with ¹¹C at the 1- or 2-position of the acetyl group or the N-methyl position of carnitine, using the enzymes acetyl CoA synthetase and carnitine acetyltransferase, are described. With a total synthesis time of 45 min, O-[1-¹¹C]acetyl CoA and O-[2-¹¹C]acetyl CoA was obtained in 60-70% decay-corrected radiochemical yield, and O-[1-¹¹C]acetyl-L-carnitine and O-[2-¹¹C]acetyl-L-carnitine in 70-80% yield, based on [1-¹¹C]acetate or [2-¹¹C]acetate, respectively. By an N-methylation reaction with [¹¹C]methyl iodide, L-[methyl-¹¹C]carnitine was obtained within 30 min, and O-acetyl-L-[methyl-¹¹C]carnitine within 40 min, giving a decay-corrected radiochemical yield of 60% and 40-50%, respectively, based on [¹¹C]methyl iodide. Initial data of the kinetics of the different ¹¹C-labelled L-carnitine and acetyl-L-carnitines in renal cortex of anaesthetized monkey (Macaca mulatta) are presented