An NADP-dependent constitutive alcohol dehydrogenase that can oxidize hexan-1-ol was detected in several Gram-positive and Gram-negative eubacteria and in two yeasts. The enzyme was purified to homogeneity from Acinetobacter calcoaceticus NCIB 8250 and from Saccharomyces cerevisiae D273-10B. The bacterial enzyme appears to be a tetramer of subunit M(r) 40,300 and the yeast enzyme appears to be a monomer of subunit M(r) 43,500. The N-terminal amino acid sequence of the bacterial enzyme has 34% identity with part of the sequence of a fermentative alcohol dehydrogenase from Escherichia coli. The pI value of the bacterial enzyme was 5.7 and the pH optimum was 10.2. Both the bacterial and yeast enzymes were shown to transfer the pro-R hydrogen to/from NADP(H). The substrate specificities of the two enzymes were similar to each other, both oxidizing primary alcohols and some diols, but not secondary alcohols. The maximum velocities of both enzymes were with pentan-1-ol as substrate and there was very low activity with ethanol; the maximum specificity constants were found with primary alcohols containing six to eight carbon atoms. Neither enzyme was significantly inhibited by metal-binding agents but some thiol-blocking compounds inhibited them. It appears that these two alcohol dehydrogenases, on prokaryotic and one eukaryotic, are structurally, kinetically and functionally different from members of the major known groups of alcohol dehydrogenases.