Using constant infusions of 3H-labeled androgens and 14C-labeled estrogens, the dynamics of androgen and estrogen metabolism have been studied in male rhesus monkeys. The mean (+/-) MCR, as measured in whole blood, for testosterone (T; 140 +/- 10 liters/day) was significantly smaller than the MCRs for androstenedione (A), estrone (E1), and estradiol (E2; 650 +/- 8, 1010 +/- 160, and 500 +/- 20 liters/day, respectively). These findings are compatible with the specific globulin binding of T in this species. The mean blood productions were 0.42 +/- 0.11 and 0.55 +/- 0.04 mg/day for A and T and 40 +/- 16 and 13 +/- micrograms/day for E1 and E2, respectively. The interconversions of the androgens [fractional conversion rates of A to T ([rho]A,TBB) and T to A ([rho]T,ABB)] were not different but were lower than the interconversions of the estrogens ([rho]E1,E2BB and [rho]E2,E1BB). The mean [rho]T,E2BB values were 0.015 +/- 0.001 and 0.0024 +/- 0.0003, which are remarkably similiar to those values in men. Administrations of PMS gonadotropin did not alter any measured values of androgen or estrogen metabolism, hCG resulted in a decrease in the conversion ratio of A to T, T administration increased the MCR of T, and estrogen administration resulted in no changes. The aromatization rate remained unaffected by all treatments.