There are very few reports of the concentration of androgens (e.g. Weinheimer, Oertel, Leppla, Baise & Bette, 1965) and oestrogens (Engel, 1962) in adrenal venous blood collected from unanaesthetized subjects. Adrenal venous blood was collected by retrograde catheterization of the right or left adrenal vein via the femoral vein in conscious subjects (Spark, Dale, Kahn & Melby, 1969). In each case a control sample was collected by allowing a free drip from a heparinized adrenal catheter. Fifteen min. after the injection of 0·25 mg. β1–24 corticotrophin (ACTH) (Cortrosyn, Organon) into a peripheral vein a further sample of adrenal venous blood was collected. Cortisol, aldosterone and 18-hydroxycorticosterone were measured as previously described (Spark et al. 1969). Testosterone, androstenedione, oestrone and oestradiol-17β were analysed on a second portion of plasma by double isotope derivative methods (Riondel, Tait, Gut, Tait, Joachim & Little, 1963; Horton, 1965; Baird, 1968). The blanks of the