Hypertension in blacks is common, often severe, and largely unexplained. Recent studies have suggested that aldosterone secretion in blacks may be reduced, whereas older data demonstrate no racial differences in aldosterone excretion. We performed this study to examine adrenal responsiveness in black hypertensive patients under controlled metabolic conditions. Thirty-one black hypertensive patients and 7 black normotensive subjects were studied on intakes of 10 mmol/d sodium and 100 mmol/d potassium, with the renin-angiotensin-aldosterone system further stimulated by upright posture or infusion of angiotensin II (Ang II). Forty-six hypertensive and 14 normotensive whites underwent the same protocol as a comparison group. Hypertensive blacks and whites had similar mean basal plasma aldosterone levels on a low salt diet, lower in both groups than in normotensive subjects. In the black patients, however, plasma aldosterone responses were significantly lower than responses in white hypertensive patients when further stimulated by either posture (1451 +/- 216 versus 2571 +/- 225 pmol/L [52.3 +/- 7.8 versus 92.7 +/- 8.1 ng/dL], P < .002) or Ang II infusion (843 +/- 122 versus 1617 +/- 189 pmol/L [30.4 +/- 4.4 versus 58.3 +/- 6.8 ng/dL], P < .001). Renin status did not account for the difference. Basal and stimulated plasma aldosterone concentrations, on the other hand, were similar in normotensive white and black subjects. Blunted adrenal responses to upright posture and Ang II infusion are common among black hypertensive patients. These abnormalities may be part of a larger constellation of abnormalities in blacks, reflecting perhaps a greater, more frequent underlying disturbance in salt handling than in whites.