The acute effects of captopril on blood pressure, renin, angiotensin, bradykinin and catecholamines were examined in patients with essential (n = 10, Group 1), accelerated (n = 6, Group 2) and renal hypertension (n = 14, Group 3). 2. Blood pressure showed little change in Group 1, fell significantly in Group 2, with a marked fall in Group 3. Heart rate did not change. 3. The fall in blood pressure was positively correlated with pretreatment renin and angiotensin II. 4. Angiotension II fell, with reciprocal increases in renin and angiotensin I. No changes occurred in bradykinin or catecholamines. 5. The rise in renin after captopril was greatest in renovascular hypertension which may prove useful as a screening test for such patients.
