An NADP(+)-dependent alcohol dehydrogenase was found in Euglena gracilis Z grown on 1-hexanol, while it was detected at low activity in cells grown on ethanol or glucose as a carbon source, indicating that the enzyme is induced by the addition of 1-hexanol into the medium as a carbon source. This enzyme was extremely unstable, even at 4 degrees C, unless 20% ethylene glycol was added. The optimal pH was 8.8-9.0 for oxidation reaction. The apparent K(m) values for 1-hexanol and NADP(+) were found to be 6.79 mM and 46.7 microM for this enzyme, respectively. The substrate specificity of this enzyme was very different from that of already purified NAD(+)-specific ethanol dehydrogenase by showing the highest activity with 1-hexanol as a substrate, followed by 1-pentanol and 1-butanol, and there was very little activity with ethanol and 1-propanol. This enzyme was active towards the primary alcohols but not secondary alcohols. Accordingly, since the NADP(+)-specific enzyme was separated on DEAE cellulose column, Euglena was confirmed to contain a novel enzyme to be active towards middle and long-chain length of fatty alcohols.