Nebulized bitolterol solution and isoproterenol solution were compared when used on a regular basis, 2.5 mg three times a day for 1 month by patients with chronic asthma. In this multicenter, double-blind trial; 130 nonsteroid-dependent patients were randomized to receive one of the two treatments concomitantly with their regular asthma medications. On study days, at the beginning of the study and after 2 and 4 weeks, treatments were given in the office or laboratory and patients were monitored with pulmonary function tests for eight hours. Both medications induced rapid bronchodilation that had a longer duration after bitolterol. The incidence of tremor was similar with the two medications. Tachycardia and palpitations were more frequent following isoproterenol. Bitolterol has a much longer duration of action and should be considered as a suitable bronchodilator for regular nebulizer treatment of chronic asthma.