Summary. In this study 51 patients with severe hypertension (20 essential, 15 renovascular and 16 renalparenchymatous) resistant to a standardized triple therapy were treated with the oral converting enzyme inhibitor captopril. Mean treatment period was 8.6 in essential, 8.9 in renovascular and 9.9 months in renalparenchymatous hypertension.In each of the 3 groups a marked and sustained blood pressure reduction was observed promptly after introducing captopril. However, absolute fall in mean blood pressure as well as individual blood pressure response were more pronounced in renovascular than in essential and in renalparenchymatous hypertension demonstrating a higher blood pressure lowering activity of the converting enzyme inhibitor in the former.In addition, our results document that monotherapy with captopril was rather the exception than the rule. More than 90% of all patients required at least the addition of a diuretic and even a substantial percentage of patients needed as a third drug a betablocker (50% in essential, 38% in renalparenchymatous and 26% in renovascular hypertension).As expected renin activity increased under captopril whereas plasma aldosterone and converting enzyme activity decreased.Side-effects (skin rash, pruritus, supraventricular extrasystoles, tachycardia, water and fluid retention, Raynaud-phenomenon, incomplete and complete taste loss and leucopenia) occurred in 17.6% (n=9) of the 51 patients.Our results show that captopril is a potent blood pressure lowering agent in severe and therapy resistant hypertension. The vast majority of patients, however, required concomitant therapy with a diuretic and/or a betablocker. Finally, the frequency of drug induced side-effects necessitates a close and careful monitoring of all patients. Unsere Resultate zeigen weiter, dab eine Monotherapie mit Captopril eher die Ausnahme als die Regel war. So ben6tigten fiber 90% der Patienten zusfitzliche Gabe eines Diuretikums und ein weiterer Anteil der Patienten darfiberhinaus die Gabe eines Betablockers (50% der Patienten mit essentieller, 38% der F/ille mit renalparenchymat6ser und 26% der Patienten mit renovaskulfirer Hypertonie).Die Plasma-Renin-Aktivitfit stieg unter Captoprilbehandlung erwartungsgemfiB an, wfihrend die Plasrna-Aldosteron-Konzentration und die Converting enzyme Aktivit~t abfielen.