The bronchopulmonary effects of celiprolol were studied in 12 male asthmatic patients who showed mean maximum changes of -24% in forced one-second expiratory volume (FEV1) and 130% in airways resistance (Raw) following a single, 80 mg dose of propranolol. Celiprolol 200 and 400 mg and placebo were administered in double-blind, random fashion. Raw and FEV1 were determined by whole body plethysmography 1, 2, and 3 h post dose. For placebo and celiprolol 200 and 400 mg, mean maximum changes in FEV1 were 0.6, 2.8, and 2.4%, and for Raw, 11.3, -0.2, and -10.9%, respectively. Pulmonary effects of the three treatments were indistinguishable but differed significantly from propranolol. Five 0.5 mg doses of terbutaline aerosol, administered at 15-min intervals starting 3 h post drug or placebo, caused less bronchodilation after propranolol than after placebo, or celiprolol 200 or 400 mg; the responses after the latter three were indistinguishable. These results suggest that celiprolol is highly bronchosparing and does not block bronchodilation following the beta 2-agonist terbutaline in propranolol-sensitive asthmatics. In contrast to classical beta-adrenoceptor antagonists, celiprolol may afford a greater margin of safety in asthmatic patients with angina or hypertension.