The hypothalamic-pituitary-gonadal axis was studied in 8 male patients with systemic lupus erythematosus (SLE), both before and after intravenous administration of luteinizing hormone-releasing hormone (LH-RH). We provide evidence herein that resting serum levels of estrone are increased and that resting serum testosterone (T) and dihydrotestosterone (DHT) levels are decreased in male patients with SLE. The decreased serum T levels were observed even after the IV administration of 25 micrograms of LH-RH. The high basal serum prolactin (PRL) levels observed in these patients with SLE is a novel finding not previously reported that could explain why serum T and DHT levels are low in this syndrome. We observed a decrease in the pituitary response to LH-RH stimulation; this low response could also be a hormonal manifestation of hyperprolactinemia. Furthermore, it has been suggested that PRL plays a role in immunocompetence, and therefore it could have influence either directly or indirectly in the altered immunoregulation observed in SLE.