Hydroxysteroid (17) dehydrogenase 2 (HSD17B2) has been shown to inactivate both estrogens and androgens and to activate 20-hydroxyprogesterone to progesterone. In the present study, we generated transgenic (TG) mice ubiquitously expressing human HSD17B2. The TG mice produced showed growth retardation and delayed eye opening at the post-natal age. Disrupted spermatogenesis was evident in the presence of normal serum and intratesticular testosterone, progesterone and normal circulating luteinizing hormone concentrations. A proper androgen action in the target tissues was confirmed by normal histological appearance of the prostate and the epididymis. Furthermore, quantitative RT-PCR analysis indicated only a slight decrease in androgen-dependent gene expression in the prostate. The disrupted spermatogenesis was not associated with increased germ cell apoptosis as analyzed by caspase-3 activation. However, it resulted in infertility in the HSD17B2TG males after the age of 3 months, and at the age of 6 months the seminiferous tubules showed a Sertoli cell only phenotype. The data indicate that the growth retardation and disrupted spermatogenesis are not due to a lack of proper estrogen or androgen action. Interestingly, the testicular phenotype and some of the other phenotypic changes described are typically observed in mice with reduced action of retinoic acid signaling. This, together with the rescue of the testis phenotype by a synthetic retinoic acid receptor agonist (TTNPB), suggests a role for HSD17B2 in the action of retinoids, in addition to its oxidative HSD17B-activity on sex steroids.