Plasma concentrations of progesterone (P), deoxycorticosterone (DOC), 17-hydroxyprogesterone (17-OH P), corticosterone (B), deoxycortisol (S), cortisol (F), and aldosterone were measured in 8 control subjects and in 10 patients with low and normal renin essential hypertension (EH) before and 4 and 8 h after an iv infusion of 25 units of ACTH. Secretion rates of 18-hydroxy-11-deoxycorticosterone (18-OH DOC) were measured for the 24 h prior to and the day of the ACTH infusions. The hypertensive patients had significantly higher plasma levels of aldosterone, DOC and S after ACTH than the controls, whereas plasma B levels were significantly lower. The low renin subgroup considered separately had significantly higher plasma levels of aldosterone and DOC than controls, and higher levels of B and lower levels of F than the normal renin subgroup in response to ACTH. Although not significantly different, the plasma levels of P and the secretion rate of 18-OH DOC tended to be higher, and plasma 17-OH P and F levels lower after ACTH in patients with EH than in controls. The low renin subgroup tended to have the highest plasma S levels and 18-OH DOC secretory rates and lowest F levels. Estimations of adrenal 11beta-hydroxylating efficiency in response to ACTH in patients and controls by plasma steroid ratios revealed significantly lower B/DOC ratios in both low and normal renin patients compared to controls, supported by somewhat lower F/S ratios in these patients, especially those in the low renin subgroup. Altered 17-hydroxylating efficiency seen by significantly lower 17-OH P/P ratios were also found in those with EH, supported by somewhat lower F/B and S/DOC ratios in these patients, agian especially in the low renin subgroup. These data are compatible with a pattern of altered adrenocortical steroid biosynthesis in essential hypertension bearing features similar to adrenal 11beta and 17alpha-hydroxylation deficiencies.