This double-blind, randomised, within patient, placebo-controlled study set out to investigate the effect of a cardioselective beta-blocker, atenolol, at different oral doses (50, 100 and 200 mg) and a non-selective agent, propranolol (40 mg), upon 1. airways resistance (forced expiratory volume at one second=FEV₁) and 2. the bronchodilator action of increasing doses of inhaled isoprenaline, in patients with co-existent hypertension and reversible airways obstruction. In 10 patients, two hours after drug administration, the 3 doses of atenolol caused a significantly greater (P<0.05) degree="" of="">₁-blockade than propranolol. In contrast the 3 doses of atenolol caused significantly less (P<0.05 to="" 0.01)="">₂-blockade as evidenced by a smaller fall in FEV₁. The isoprenaline FEV₁ dose response curves were displaced progressively to the right of the placebo curve with increasing doses of atenolol, but the greatest displacement was with propranolol. It was concluded that patients with reversible airways obstruction who require beta-blockade should be given a low dose of a cardioselective agent in conjunction with, if required, a beta₂ stimulant such as isoprenaline. Such a treatment will be less likely to cause a troublesome increase in airways resistance and the bronchodilator action of the beta₂ stimulant will be almost fully preserved.