The effects of two cardioselective beta-adrenergic blocking agents--celiprolol (claimed to have bronchodilator properties) and atenolol (without such claims)--on respiratory function and control of asthma were studied in ten asthmatic patients with mild to moderate essential hypertension. Following a beta-2 agonist-free period of ten hours, administration of 100 mg of atenolol was associated with bronchoconstriction (p less than 0.05), whereas 400 mg of celiprolol was not. Responsiveness to beta-2 agonist therapy was retained with both agents (p less than 0.05). Day-to-day asthma control, interpreted from patient recordings of peak flow, inhaler use and symptom scores, were all no different on either agent from placebo. When given acutely, celiprolol appeared to have acute bronchosparing properties, possibly providing a greater margin of respiratory safety than atenolol.