Formoterol, a new beta 2-agonist, and salbutamol were given as aerosols twice and four times daily, respectively, to patients with reversible obstructive lung disease. The study was controlled and double blind, and continued for 12 weeks. Ninety-nine patients from five study centers were included and 89 patients could be properly evaluated. The formoterol-treated patients used significantly less rescue medicine (salbutamol aerosol) and had higher morning PEF values. For the other efficacy variables (daytime FEV1.0, evening PEF, patient and investigator global evaluations, night sleeping time) and tolerance (side effects noted by patients, blood and urine laboratory values, ECG, patient and investigator global evaluation), there were no significant differences between the formoterol- and the salbutamol-treated groups.