Dilevalol combines a nonselective blocking action on beta-receptors with selective beta 2-agonist activity. In this double-blind, three-way, crossover study, the effects of relatively high single doses of dilevalol (400 mg), metoprolol (200 mg), a placebo on pulmonary function and their interaction with isoproterenol (160 and 480 micrograms) were evaluated in 16 patients with reversible bronchial asthma [isoproterenol-induced increase in forced expiratory volume in 1 s (FEV1) of greater than or equal to 15%]. When the lowest or minimum values observed during the 2 h postdrug evaluation period were considered, there was no significant difference from baseline in the percentage change in FEV1 after placebo (-4.4%) and dilevalol (-10%), with the difference between these treatments not being statistically significant. However, following metoprolol, FEV1 decreased by 18.3%, a decrease significantly different (p less than 0.01), from baseline and from the effects of placebo (p less than 0.01), although not from dilevalol. Furthermore, following metoprolol, 7 of 16 patients (44%) showed a greater than or equal to 20% decrease in FEV1 as compared to only 3 patients (19%) following dilevalol and 1 patient (6%) following placebo. The effects of the three treatments on forced vital capacity (FVC) and maximal midexpiratory flow (MMEF) were qualitatively similar to those observed in FEV1. Both dilevalol and metoprolol similarly and significantly (p less than or equal to 0.01) inhibited the isoproterenol (160 and 480 micrograms) response in FEV1 as compared to placebo.(ABSTRACT TRUNCATED AT 250 WORDS)