The quantities of corticoids and sex steroids were determined in the adrenal effluent plasma from ovariectomized rhesus monkeys. The effects of ACTH (20 IU), Metopirone (30 mg/kg), and Metopirone + dexamethasone infused over a 4½-hr period on the amount of steroid found in plasma collected over a 30-min period were compared with saline-infused controls. ACTH (Armour Acthar) did not affect any of the steroids monitored in the adrenal effluent. Metopirone significantly blocked the amount of Porter-Silber chromogen/min (4,450 ng/min in control, 410 ng/min in Metopirone treated, p < 0.01) but did not affect the quantities of progesterone, estrone, or estradiol. Significant elevations in both testosterone (0.28 ng/min in control, 1.72 ng/min in Metopirone treated) and androstenedione (6.72 ng/min in control, 33.44 ng/min in Metopirone treated) were observed after treatment with Metopirone (p < 0.01). The data show the relative quantities of sex steroids to corticoids in adrenal effluent plasma. They also demonstrate that the blockade of cortisol synthesis results in the elevation of androgen but not of progesterone. A comparison was made between the quantities of progesterone, androgen, and estrogen in the systemic plasma and in plasma from the adrenal vein. The average of 14 determinations of progesterone in adrenal effluent plasma was 11.5 ± 3.3 (se) ng/ml. In systemic plasma only 1 of 14 samples showed detectable quantities. Androstenedione on the other hand, was 34 times more concentrated [25.8 ± 4.0 (se) ng/ml] in the adrenal venous compared to [0.7 ± 0.2 (se) ng/ml] systemic plasma. Testosterone was 2½ times greater in the adrenal vein [0.5 ± 0.1 (se) ng/ml] compared to samples drawn from the periphery [1.3 ± 0.3 (se) ng/ml]. The concentration of estradiol-17β and estrone in systemic plasma were rarely above the lower limits of the assay. In plasma from the adrenal vein 0.051 ± 0.018 (se) ng/ml and 0.134 ± 0.020 (se) ng/ml were found respectively. The data suggest that progesterone in the systemic plasma pool is rapidly metabolized and not augmented by conversions from other compounds. Testosterone on the other hand is formed by peripheral conversions from other compounds that significantly affect the size of the testosterone pool in systemic plasma.