We have examined the effects of 7 days treatment with beta adrenoceptor antagonists in 8 healthy volunteers in a placebo controlled, crossover study. We investigated three beta-adrenoceptor antagonists (atenolol, oxprenolol, and propranolol), which have differing profiles of selectivity and partial agonist properties (intrinsic sympathomimetic activity, ISA). We studied adrenaline-induced hypokalaemia, the vasodilator response to an infusion of adrenaline (0.06 micrograms X kg-1 X min-1 for 90 min), and lymphocyte beta 2-adrenoceptor number, determined by (-) [125I]-iodocyanopindolol binding, and measured these variables both before and after 7 days of treatment. The beta 2-mediated depressor response to adrenaline infusion was abolished by propranolol and oxprenolol but persisted after atenolol. In contrast, the hypokalaemia induced by adrenaline was abolished by all three beta-blockers. Lymphocyte beta 2-adrenoceptor number increased significantly following propranolol treatment, but not after oxprenolol for atenolol. We conclude that up-regulation of lymphocyte beta 2-adrenoceptors is dependent on beta 2-receptor blockade and is modified by ISA. The reversal of the hypokalaemic response by atenolol suggests that beta 1 receptors may contribute to the former effect. Alternatively, since different populations of beta 2-adrenoceptors differ in their susceptibility to antagonists there may also be differences in agonist coupling to beta 2-responses between tissues.