Serum concentrations of luteinizing hormone, follicle-stimulating hormone, prolactin, 17 beta-estradiol, testosterone, androstenedione, dehydrotestosterone, dehydroepiandrosterone sulfate, and cortisol were examined in 14 men with rheumatoid arthritis (RA) and in age-matched osteoarthritis controls. Hypophyseal, adrenal, and testicular responses to stimulation with luteinizing hormone-releasing hormone, adrenocorticotropin, and human chorionic gonadotropin, respectively, were evaluated in 8 RA patients and in 8 age-matched healthy volunteers. Basal serum testosterone concentrations were significantly lower in male RA patients than in the osteoarthritis control subjects (P less than 0.01). After human chorionic gonadotropin stimulation, serum concentrations of testosterone were also lower in the RA patients than in normal healthy controls (P less than 0.05). These findings suggest that diminished testicular steroid biosynthesis might contribute to the serum testosterone deficiency observed in male RA patients.