T he secretion of androgens and estrogens by normal and abnormal testes was compared by determining the concentrations of dehydroepiandrosterone (DHEA), androstenedione (Δ₄A), testosterone (T), estrone (E₁), and 17β-estradiol (E₂) in peripheral and spermatic venous plasma samples from 14 normal men and 5 men with unilateral testicular atrophy. Four normal men and one patient with unilateral atrophy of the testis were given human chorionic gonadotropin (HCG) before surgery. Plasma estrogens were determined by radioimmunoassay; plasma androgens were measured by the double-isotope dilution derivative technique. Peripheral concentrations of these steroids before and after HCG were similar in both the normal men and the patients with unilateral testicular atrophy. In normal men, the mean ±SE spermatic venous concentrations were DHEA, 73.1±11.7 ng/ml; Δ₄A, 30.7±7.9 ng/ml; T, 751±114 ng/ml; E₁, 306±55 pg/ml; and E₂, 1298±216 pg/ml. Three of four subjects with unilateral testicular atrophy had greatly diminished spermatic venous levels of androgens and estrogens. HCG treatment increased the testicular secretion of DHEA and T fivefold, Δ₄A threefold, E₁ sixfold, and E₂ eightfold in normal men. In the single subject with an atrophic testis who received HCG, the spermatic venous concentrations of androgens and estrogens were much less than in normal men similarly treated. We conclude that: (a) E₁ is secreted by the human testis, but testicular secretion of E₁ accounts for less than 5% of E₁ production in normal men; (b) HCG stimulation produces increases in spermatic venous estrogens equal to or greater than the changes in androgens, including testosterone; and (c) strikingly decreased secretion of androgen and estrogen by unilateral atrophic human tests cannot be appreciated by analyses of peripheral steroid concentrations.