S-9780 is the active diacid metabolite of the new angiotensin-converting enzyme (ACE) inhibitor perindopril. In a double-blind, randomised, crossover study, the effects of 1, 2, and 4 mg of S-9780 administered intravenously (i.v.) were compared with placebo in eight normotensive subjects. All active doses caused immediate, maximal, and similar inhibition of plasma ACE with 40% inhibition persisting after 48 h. Plasma renin activity was elevated 4 and 8 h after dosing, but no effect on plasma aldosterone, adrenaline or noradrenaline levels was detected. Diastolic blood pressure was lowered by 4 mg of S-9780 until 24 h after dosing. Heart rate did not change. The pharmacokinetics of S-9780 fitted a three-compartment model with a terminal half-life (t1/2) of 31 h. Inhibition of plasma ACE was closely related to observed drug concentration, with 1.8 +/- 0.9 ng/ml (mean +/- S.D.) producing 50% inhibition of the enzyme. S-9780 caused predictable effects on the cardiovascular and renin angiotensin systems.