We have isolated an NADPH-dependent reductase from neonatal pig testes that metabolizes androgens and a variety of xenobiotics. This enzyme is distinct from 3alpha/beta,20beta-hydroxysteroid dehydrogenase or its homologue, carbonyl reductase, as judged by its immunological and molecular properties and its much narrower specificity for steroids. This reductase and 3alpha/beta,20beta-hydroxysteroid dehydrogenase may be part of a mechanism for regulating androgen levels the neonatal pig testes. Interestingly, we could not find multiple isoforms of 3alpha/beta,20beta-hydroxysteroid dehydrogenase/carbonyl reductase in pig testes unlike human and rat testes and other organs in which multiple isoforms are expressed.