Activities of the polyol dehydrogenases of Puccinia graminis f. sp. tritici were surveyed by measuring polyoldependent rates of reduction of NAD+ and NADP+ in cell-free extracts of axenically-grown mycelia. Seven of the eight polyols tested caused NADP+ reduction, with highest activity for D-glUcitOl, followed by L-arabitol, xylitol, erythritol, galactitol and ribitol, and low activity with D-arabitol; only D-mannitol failed to support activity. Inactivation rates were consistent with at least three separate enzymes, specific for D-ghcitol, xylitol and L-arabitol respectively, with apparent K, values of 170-198mM for xylitol and D-glUCitOl (K, for NADP+
36-55 p~) ,and 34 mM for L-arabitol ( K , for NADP+ 1.2 p~) .The NADP+-dependent activities were almost completely inhibited by 2 mM-dithiothreitol, in contrast to the NAD+-dependent activities, which were stimulated. NAD+-dependent activity was highest with D-mannitol, followed by successively lower activities with D-arabitol, xylitol and D-ghcitol, with no activity with any of the other polyols; each of the four active polyols appeared to be oxidized by a different enzyme. All four NAD+-dependent activities were rapidly lost after Sephadex treatment of crude extracts.