Because of previous contradictory results, we reevaluated the effects of tamoxifen on 29 men presenting with idiopathic oligozoospermia. To determine whether a possible increase in sperm concentration might be correlated with an improvement of sperm quality, the hamster ovum penetration (HOP) test and the hypo-osmotic swelling (HOS) test were included as additional tests of sperm function. Patients were treated with tamoxifen (20 mg/day) for 3 months. From 4 weeks until the end of the study, tamoxifen had a significant effect (P < 0.001) on blood levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T), and estradiol (E2). Prolactin (PRL) concentrations were not altered significantly (P > 0.05). There was no significant improvement (P > 0.05) of conventional semen parameters (volume, concentration, motility, morphology), and of HOP and HOS test results. The lack of correlation between a rise in hormone levels and improvement of sperm quality suggests that tamoxifen is of questionable value in men with idiopathic oligozoospermia.