Hypertension was induced in marmosets by ligating the minor branch of one renal artery. The blood pressure (BP), measured by a tail-cuff method, increased to hypertensive levels within 4-5 weeks and the maximum increases occurred after 4-15 weeks (BP, mean +/- s.e.m. was 120 +/- 3 and 152 +/- 6 mmHg before and 10 weeks after ligation, respectively; n = 9). There was a small increase in plasma renin activity (PRA) after 2 weeks, but PRA decreased thereafter and there was no correlation between PRA and BP. The renin inhibitor CGP 29,287 (Ciba-Geigy Ltd., Basle, Switzerland, synthesized by D.B. Rinker and P. Bühlmayer; 1 mg/kg i.p.) and the angiotensin converting enzyme (ACE) inhibitor, enalaprilat (Merck Sharp and Dohme, USA.; 2 mg/kg i.p.), lowered the BP of the hypertensive marmosets to normotensive levels. These results indicate that although PRA is not elevated in this primate model of hypertension, BP is dependent on the activity of the renin-angiotensin system.