3(or 17)alpha-hydroxysteroid dehydrogenase (, 3(17)alpha-hydroxysteroid dehydrogenase) is an enzyme with systematic name 3(or 17)alpha-hydroxysteroid:NAD(P)<sup>+</sup> oxidoreductase. This enzyme catalyses the chemical reaction
This enzyme acts on the 3alpha-hydroxy group of androgens of the 5alpha-androstane series; and also, more slowly, on the 17alpha-hydroxy group of both androgenic and estrogenic substrates (cf. EC 1.1.1.51 3(or 17)beta-hydroxysteroid dehydrogenase).