1 In a double-blind study, 36 patients with essential hypertension were randomly allocated to treatment with either metoprolol, 100--300 mg/day, or pindolol, 5--15 mg/day for 6 months. Haemodynamic investigations were made on three separate occasions. Blood flow in the calves and in the forearm was determined by venous occlusion plethysmography after 6 weeks of placebo, after 6 weeks and again after 6 months of active therapy. 2 Both drugs reduced blood pressure significantly, by 17.1/11.8 mm Hg with metoprolol and 21.9/10.9 mm Hg with pindolol after 6 weeks (P less than 0.005). No further changes were seen after 6 months. 3 Heart rate after 6 weeks was significantly reduced by metoprolol (10.7 +/- 2.4 beats/min, P less than 0.001) but not by pindolol (4.4 +/- 2.3 beats/min, NS). After 6 months a significant reduction was seen also in the pindolol group (5.2 +/- 2.1 beats/min, P less than 0.05). 4 The vascular resistance in the calves at rest was reduced by pindolol (P less than 0.05), whereas resistance tended to increase with metoprolol. 5 Resting vascular resistance in the forearm after 6 months was significantly reduced in the metoprolol group (P less than 0.001) as well as in the pindolol group (P less than 0.02). The increase in forearm vascular resistance seen during leg exercise was not influenced by either drug. 6 Vascular resistance at maximal vasodilatation was unchanged in the calves, but a significant reduction (-17.4 +/- 5.7%, P less than 0.01) in the forearm vascular bed was seen after 6 months of pindolol. No change was observed with metoprolol. 7 It is concluded that pindolol reduces elevated blood pressure partly through peripheral vascular mechanism. Metoprolol, on the other hand, probably acts mainly via central cardiac mechanisms.