1. The effects on glucose and lipid metabolism and on plasma catecholamines at rest and during exercise, of 4 weeks treatment with non-selective beta-blockade (pindolol, 15 mg daily) and with cardio-selective blockade (metoprolol, 200 mg, and acebutolol, 500 mg, respectively) were compared in different groups of hypertensive men (mean age 37 years) by single blind cross-over technique. All patients continued the treatment with either metoprolol or acebutolol for another 12--14 months. 2. All antagonists reduced blood pressures and exercise heart rates in a virtually identical manner. Whereas lipolysis was similarly inhibited by both selective beta 1-antagonists and non-selective beta 1-beta 2-blockers, glycogenolysis in the muscle was inhibited only by non-selective beta-receptor blockade. 3. The inhibition of glycogen breakdown resulted in exercise hypoglycaemia and in increases of plasma adrenaline and ACTH, which probably reflect counter-regulatory mechanisms. No major metabolic changes occurred after 12--14 months compared with 4 weeks of treatment.