BW A575C (N‐(1‐(S)‐carboxy‐5‐[4(3‐isopropylamino‐2‐(R, S)‐hydroxypropoxy)indole‐2‐carboxamido]pentyl)‐(R, S)‐alanyl‐(S)‐proline) is a chemically novel agent which exhibits in a single molecule both angiotensin converting enzyme (ACE) inhibition and β‐adrenoceptor‐blocking properties. BW A575C produced a competitive blockade of heart rate responses to isoprenaline in a guinea‐pig right atrial preparation (pKB 7.18 ± 0.05, cf. pindolol 8.9 ± 0.7). BW A575C inhibited a partially purified preparation of ACE obtained from rabbit lung (IC50 10.7 ± 2.1 nm, cf. enalaprilat, 4.4 ± 0.8 nm). Intravenous administration of BW A575C (1–100 μg kg−1 min−1) to the pithed rat inhibited in a dose‐dependent fashion both angiotensin I‐induced pressor responses and isoprenaline‐induced tachycardia. Dose‐ratios obtained from such studies demonstrated that, in this preparation, BW A575C was approximately 100 times more active as an ACE inhibitor than as a β‐adrenoceptor blocking agent. Intravenous administration of BW A575C (1 mg kg−1) to the conscious rat inhibited angiotensin I‐induced pressor responses, being approximately equipotent to enalapril and 10 times more potent than captopril. At the same dose, BW A575C had a similar duration of action as an ACE inhibitor to enalapril. Intravenous administration of BW A575C (1 mg kg−1) to either conscious dogs or rats inhibited both angiotensin I‐induced pressor responses and isoprenaline‐induced heart rate responses. Dose‐ratios obtained from such studies demonstrated that in these species, BW A575C was 2–10 times more active as an ACE inhibitor than as a β‐adrenoceptor blocking agent.