Responsible for the reduction of the oxo group on the C-3 of 5alpha-androstane steroids. Catalyzes the conversion of dihydrotestosterone to its inactive form 5alpha-androstanediol, that does not bind androgen receptor/AR. Does not function as an isomerase. a 3beta-hydroxysteroid + NADP(+) = a 3-oxosteroid + H(+) + NADPH 5alpha-androstane-3beta,17beta-diol + NADP(+) = 17beta-hydroxy-5alpha-androstan-3-one + H(+) + NADPH Steroid metabolism. Expressed in the male liver, starting in late puberty. Belongs to the 3-beta-HSD family.