The purpose of this study was to investigate the effects of repeated administrations of ACTH 1-17 (Syncrodyn 1-17) on sexual and endocrine function in men with psychogenic impotence. Twenty adult impotent men from 21 to 48 years volunteered for this study; organic causes of erectile impotence were excluded in each subject. Ten subjects were treated with ACTH 1-17 (100 micrograms i.m. daily for 15 days during 6 consecutive months), whereas saline was injected in the control group (10 subjects) following the same protocol. Clinical and endocrine evaluation were performed before and at the end of treatment. Serum levels of LH, FSH, PRL, testosterone (T) and cortisol were measured by RIA methods. To investigate diurnal rhythms of T and cortisol, blood samples were taken at 0800 and at 1800. In ACTH 1-17-treated men a significant improvement in sexual function was shown when compared with the control group (p less than 0.05); moreover, both anxiety and fatigability were lowered by ACTH 1-17 administration. ACTH 1-17 did not affect basal levels of LH, FSH, PRL, T and cortisol, whereas the diurnal variation of T, which was absent before treatment in both treated and control group, was restored. No changes in clinical and endocrine parameters were shown after placebo injections. Our data emphasize that the chronopharmacological action of ACTH 1-17 may positively affect sexual function and circadian T rhythmicity in men with psychogenic impotence.