In recent years evidence has accumulated which indicates that although various beta-adrenoceptor antagonists are equally effective in lowering blood pressure in patients with essential hypertension the mechanisms of action of the different drugs are heterogeneous. 2. Pindolol, a beta-adrenoceptor antagonist with pronounced intrinsic sympathomimetic activity (ISA) appears, to some extent, to act via peripheral vascular mechanisms. 3. Following prolonged treatment with pindolol in essential hypertension peripheral vascular resistance at maximal vasodilatation has been found to be decreased compared with the pretreatment values suggesting that the structural vascular changes characteristic of established hypertension may be reversible.