A radioimmunoassay technique for the simultaneous measurement of eight unconjugated steroids (progesterone, pregnenolone, dehydroepiandrosterone, androstenedione, testosterone, dihydrotestosterone, oestrone and oestradiol) in the peripheral plasma of human males is described. Determinations of these steroids and of immunoreactive FSH and LH were carried out on the plasma of twenty-one normal individuals and the levels were compared to those of eleven and ten males exhibiting oligospermia and azoospermia, respectively. Mean values and tolerance limits for each hormone, based on a lognormal distribution of individual values, are presented for all groups. Oligospermia was associated with a significant reduction in plasma dihydrotestosterone and testosterone levels. Azoospermic subjects also exhibited decreased dihydrotestosterone levels but a normal range of testosterone concentrations. Mean peripheral plasma levels of FSH were significantly elevated in both pathological groups and this was paralleled in the azoospermic men by increased concentrations of plasma LH.