Objective: The respiratory effects of nebivolol, a new selective beta (1)-adrenergic blocking agent, and celiprolol, a beta -blocker possessing strong beta (1)-adrenoceptor antagonist and mild beta (2)-agonist properties, were investigated in 12 patients with mild asthma. Design: Changes in several spirometric indexes (FVC, FEV1, and forced expiratory flow rate at 50% of FVC) were measured. The interaction with the bronchodilator effect of the beta (2)-adrenoceptor-selective agonist albuterol also was investigated. Results: The effect of both nebivolol and celiprolol on FEV1 was considered to be significant (p < 0.05). The administration of nebivolol and celiprolol, but not of placebo, elicited a decrease in FEV1: mean maximum difference for nebivolol, -0.272 L (95% confidence interval [CI], -0.402 to -0.142); mean maximum difference for celiprolol, -0.193 L, (95% CI, -0.316 to -0.071); mean maximum difference for placebo, -0.0001 L (95% CI, -0.081 to 0.085). The inhalation of albuterol, up to a dose of 800 <mu>g, significantly (p < 0.05) improved FEV1, but the values after nebivolol and celiprolol administration were lower than the initial values. Both <beta>-blockers caused equal changes in heart rate, systolic BP, and diastolic BP. Conclusions: There were no significant differences between the respiratory actions of the two active drugs.