• Plasma estrone, dihydrotestosterone, luteinizing hormone (LH), and percentage-free testosterone levels were determined in 26 predominantly or exclusively homosexual males (20 to 33 years of age) and in an age-matched control group. Although the homosexual and control groups showed a broad overlapping for all hormonal factors measured, highly significant differences between the groups were found without exception. The medians of the homosexual group (control group) and the significance levels for the two-sample rank tests were as follows: estrone 3.07 (2.43) ng/100 ml, p <.01; dihydrotestosterone 66.0 (49.2) ng/100 ml, p <.01; percentage-free testosterone 10.7% (9.7%), p <.02; LH 35.1 (24.9) ng/ml, p <.001. These findings can in part be explained by the higher LH secretion in the homosexual subjects.