Favors the reduction of androstenedione to testosterone. Uses NADPH while the two other EDH17B enzymes use NADH. Androgens such as epiandrosterone, dehydroepiandrosterone, androsterone and androstanedione are accepted as substrates and reduced at C-17. Can reduce 11-ketoandrostenedione as well as 11beta-hydroxyandrostenedione at C-17 to the respective testosterone forms.