Hormonal and mean arterial pressure (MAP) responses to posture, isometric handgrip, angiotensin II (AH), adrenocorticotrophic hormone (ACTH), and metoclopramide (MCP), a dopamine (DA) antagonist, were examined in nine men with essential hypertension and nine age- and weight-matched normotensive men on a constant 100 mEq sodium and 80 mEq potassium intake before and after 4 days of administration of the DA agonist, bromocriptine (BEC; 2.5 mg three times a day). BEC depressed supine basal MAP in the hypertensives, and decreased MAP response to posture and isometric exercise in both groups. There were similar reductions (p< 0.01) in basal supine norepinephrine (NE) in the two groups. Hypertensives displayed greater (p< 0.01) NE responses to posture and exercise than the normotensives. BEC decreased the NE response to 10 minutes of upright posture and exercise more in hypertensives (p< 0.01) than in normotensives. Hypertensives had greater (p< 0.05) plasma aldosterone (PA) responses to exercise than normotensives, but following BEC, the responses were similar. BEC did not affect basal PRA or PRA responses to posture and exercise in the two groups. PA responses to ACTH and MCP were similar in both groups, but the hypertensives displayed greater (p< 0.01) PA responses to AH. BEC suppressed PA responses to AH (p< 0.01) and to high dose ACTH (p< 0.05) to a similar extent in both groups. The prolactin as well as the PA response to DA antagonism with MCP was similar in the two groups. These results suggest that dopaminergic control of NE secretion may be altered in essential hypertension. Blood pressure lowering effects of BEC in patients with essential hypertension may be related, in part, to depression of sympathetic nervous system activity. (Hypertension 4: 424–430, 1982)