Serum total testosterone, total 17 beta-estradiol, LH, FSH, and PRL concentrations were measured by RIA in 59 homosexual men infected with the human immunodeficiency virus (32 clinically healthy antibody-positive men (HH+), 20 men with acquired immune deficiency syndrome (AIDS), and 7 men with AIDS-related complex (ARC). The results were compared with those of 26 antibody-negative homosexual men (HH-) who served as controls. The mean serum total testosterone concentration was significantly lower in the men with AIDS [414 +/- 230 (+/- SD) ng/dL (14.5 +/- 8.0)] than in the HH- men [550 +/- 172 ng/dL (19.0 +/- 6.0 nmol/L); P less than 0.05]. The mean serum LH level was significantly higher in the men with AIDS (26 +/- 14 vs. 14 +/- 4 IU/L in HH- men; P less than 0.01) and slightly but significantly higher in the men with ARC (19 +/- 8 IU/L; 0.10 greater than P greater than 0.05). Serum FSH also was significantly higher in the men with AIDS (P less than 0.05). Serum PRL was significantly higher in the men with ARC (10 +/- 2 micrograms/L; P less than 0.05) and AIDS (16 +/- 10 micrograms/L; P less than 0.001) than in the HH- men (8 +/- 3 micrograms/L). Serum sex hormone-binding globulin levels were similar in HH- men and men with AIDS as were serum T responses to hCG administration for 2 days. These results suggest that alterations of the hypothalamic-pituitary-gonadal axis indicative of primary hypogonadism accompany human immunodeficiency virus infection in homosexual men.