The invention relates to novel polypeptides which have the biological activity of an NAD- or NADP-dependent alcohol dehydrogenase. The invention furthermore relates to nucleic acids encoding said polypeptides, to nonhuman hosts or host cells and to reaction systems which may be used for preparing desired products. The polypeptides of the invention are preferably used in the preparation, starting from aldehydes or ketones, of primary and enantiomerically pure secondary alcohols which may serve as intermediates for medicaments. Alternatively, the polypeptides of the invention may also be employed in the reverse reaction, i.e. the oxidation of alcohols with the formation of aldehydes or ketones.