1. By substituting one anti-hypertensive drug for the other in a panel of hypertensive patients equipotent doses have been determined. 2. Thus 40 mg of propranolol is equivalent to 4·5 mg of pindolol, 98 mg of practolol, 128 mg of alprenolol, 49 mg of metoprolol, 42 mg of tolamolol and 4·4 mg of timolol. 3. Bendorfluazide (10 mg) is eqivalent to 1·6 mg of bumetanide, 20 mg of chlorthalidone, 35 mg of mefruside and 3·5 mg of amiloride together with 35 mg of hydrochlorthiazide. 4. Methyldopa (250 mg) is equivalent to 6 0 mg of debrisoquine and 0·5 mg of St 600 (Boehringer), which is a clonidine-like substituted imidazoline.