Three months of tamoxifen treatment of 43 men with idiopathic oligozoospermia, out of which 20 completed the study, resulted in a significant enhancement of sperm motility, but the improvement of sperm parameters was in no relation to the FSH response to short time tamoxifen treatment. There was a significant increase of testosterone, estradiol, LH, FSH, SHBG, 17 alpha-hydroxy-progesterone and also of 11 beta-hydroxyandrostenedione, an androgen of exclusively adrenal origin, during the treatment and (with the exception of the latter), on the first week after discontinuation of the therapy. Significantly elevated testosterone and SHBG concentrations were retained still 9 weeks after finishing of the therapy. The results confirm that tamoxifen treatment provides conditions more favourable for conception and demonstrate that also adrenal steroidogenesis is positively influenced by this antiestrogen.