Basal LH, FSH, 17 beta-oestradiol and testosterone and the gonadotrophin responses to luteinizing hormone releasing hormone (LHRH) were studied in male patients with leprosy (twenty-four with lepromatous and six with tuberculoid leprosy). The mean basal LH and FSH was significantly elevated in the lepromatous group and was associated with an excessive response of both gonadotrophins following LHRH administration. The mean basal testosterone and 17 beta-oestradiol values in the lepromatous group were significantly lower than those of the tuberculoid and control groups. The abnormal gonadotrophin and sex steroid values in the lepromatous group are in keeping with the testicular atrophy and gynaecomastia accompanying this form of leprosy. However, the lack of a significant correlation between basal FSH and testicular atrophy should be noted. In addition, no correlation between any of these hormonal values and gynaecomastia could be demonstrated. The patients with tuberculoid leprosy had essentially normal hormonal profiles (except for two who had raised 17 beta-oestradiol values). This is compatible with the lack of gonadal involvement in these patients.