D-Carnitine was converted to L-carnitine by resting and permeabilized cells as well as with purified stereospecific carnitine dehydrogenases from Agrobacterium sp. With permeabilized cells only 11% of D-carnitine was converted into L-carnitine. Using highly stereospecific D- and L-carnitine dehydrogenases from Agrobacterium sp. (pH 8.5, 50 mM D-carnitine, 1 mM NAD(+), 0.1 mM NADH, 25-fold excess of L-carnitine dehydrogenase) almost 50% of the D-carnitine could be converted into L-carnitine.