The pharmacokinetics and pharmacodynamics of the prodrug ramipril and its active ACE-inhibiting metabolite ramiprilat were investigated in an open, randomised, three-way cross-over study in 12 healthy male volunteers. Subjects received 2.5 mg ramipril orally, 2.5 mg ramipril intravenously and 2.5 mg ramiprilat intravenously. The absolute bioavailability as judged by ramipril plasma AUC was 15%, by ramiprilat plasma AUC, 44%. Ramiprilat formation from intravenous ramipril was 53% and from oral ramipril 28%. Urinary recovery of oral ramipril was 23%, i.v. ramipril 49%, and i.v. ramiprilat 68% of the given dose. Maximum ACE inhibition was highest (100%) after i.v. ramiprilat; it was 99% after i.v. ramipril and 84% following oral ramipril. ACE inhibition over 24 h was highest after i.v. ramipril, 2% less with i.v. ramiprilat and 34% less with oral ramipril. Ramiprilat renal clearance was concentration dependent. The biological availability of ramipril can best be judged by ramiprilat AUC, urinary recovery of ramipril and metabolites, or ACE inhibition over 24 h. It is concluded that the bioavailability of oral ramipril seems to be in the range of 44-66%.