<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>The ratio of urinary testosterone (T) to epitestosterone (EpiT) is used to detect T abuse in sport. Also, plasma or urinary concentrations of EpiT have been measured to assess testicular steroidogenesis during hormonal male contraception. Further investigations are required to evaluate the relative contributions of the testis and adrenal to EpiT production. To this purpose, we have compared basal urinary EpiT glucuronide and plasma EpiT and the response to synthetic adrenocorticotrophic hormone (ACTH) stimulation between eugonadal and hypogonadal men.</jats:sec><jats:sec><jats:title>DESIGN AND SUBJECTS</jats:title><jats:p>The basal urinary excretion rate of EpiT glucuronide was determined in 34 eugonadal men. Six men, clinically diagnosed as hypogonadal, and 6 out of the 34 eugonadal men previously described, received an intramuscular injection of synthetic ACTH depot (1 mg) at 0800 h on two consecutive days. Blood samples were collected prior to and then at 1.5, 8, 24, 25.5, 32 and 48 h with respect to the first administration (0 h). 24‐h urine specimens were collected from 0800 h on days 1 and 2 (baseline) and 3 and 4 (stimulation).</jats:sec><jats:sec><jats:title>MEASUREMENTS</jats:title><jats:p>Plasma EpiT, T and cortisol were measured by RIA and urinary EpiT and T, following glucuronide hydrolysis, by gas chromatography‐mass spectrometry (extract combines aglycones with a minor amount of urinary free steroids).</jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>Basal excretion rates of EpiT glucuronide in eugonadal men (range:62–751 nmol/24 h) were considerably greater than in hypogonadal men (range: 3–34 nmol/24 h). Mean basal plasma EpiT in eugonadal men (1.32 ± 0.08 nmol/l) were greater than in hypogonadal men (0.68 ± 0.04 nmol/l). In each group, synthetic ACTH stimulation increased plasma cortisol 4‐fold. In eugonadal men, plasma and urinary EpiT were unchanged whereas plasma and urinary T glucuronide decreased in response to ACTH. In hypogonadal patients, ACTH increased plasma and urinary EpiT while plasma T remained unchanged.</jats:sec><jats:sec><jats:title>CONCLUSION</jats:title><jats:p>The testes are the major source of epitestosterone, the adrenal contribution being relatively modest. Following adrenal stimulation, urinary epitestosterone glucuronide increases considerably in hypogonadal men but this increase is masked in eugonadal men because testicular production is probably suppressed by the ACTH‐induced rise in cortisol. Activation of the adrenal cortex results in no change or only a small decrease in the urinary T/EpiT ratio in eugonadal men.</jats:sec>