Plasma basal levels of FSH, LH and total as well as apparent free testosterone were determined in homosexual and heterosexual males. Significantly higher FSH concentrations (mean +/- SD = 6,89+/-5.00 mlU/ml; P less than 0.01) and LH concentrations (28.2+/-30.7 mlU/ml; P less than 0.002) were found in plasma of 50 homosexual males compared with those of 24 or 40 heterosexual males 4.17 +/- 2.34 mlU/ml and 12.6 +/- 7.6 mlU/ml, respectively). Significantly lower free plasma testosterone was observed in 35 homosexual males (10.7 +/- 3.3 ng/100 ml; P less than 0.01) than in 38 heterosexual males (13.3 +/- 4.5 ng/100 ml), whereas total testosterone in plasma of homosexual males (590 +/- 148 ng/100 ml) showed no significant difference in comparison with the heterosexual control group (562 +/- 126 ng/100 ml). The tendency to higher FSH and LH values as well as to lower free testosterone concentrations in plasma compared with the heterosexual control group was more evident for effeminized than for non-effeminized homosexual males. FSH and LH concentrations in plasma of 5 transsexual males were also significantly higher (11.74 +/- 5.06 and 18.3 +/- 3.4 mlU/ml, respectively; P less than 0.02) than those of the heterosexual control group. Our findings may be explained by the possible existence of a prenatal testicular androgen deficiency in homosexual males that is widely compensated by increased gonadotrophin secretion in adult life.