The aim of this study was to evaluate the bronchodilating activity and the tolerability of broxaterol (B, CAS 76596-57-1) given as drops by inhalation after single administration at different doses and after repeated administrations for 1 month. Two groups of 12 patients each were treated in a double-blind fashion and according to a within-subject design: one group with B at the single doses of 1.25 mg and 2.50 mg and with placebo (P), and the other with B at the dose of 0.75 mg and with P. A further group of 12 patients was treated in open fashion for 1 month with B at the dose of 1.25 mg 3 times a day. On each study day for the single doses and on the 1st and 30th days for the repeated doses, forced vital capacity (FVC), forced expiratory volume (FEV1), maximal middle expiratory flow (MMEF), heart rate (HR) and systolic and diastolic blood pressure (BP) were measured immediately before and 15, 30, 60, 120 and 240 min after the conclusion of the treatment. At the beginning and at the end of the 1-month treatment period, haematology and biochemistry were checked. After B 0.75 mg, 1.25 mg and 2.50 mg the values of spirometric variables proved significantly and dose-dependently higher than the basal values. The changes from baseline in lung function test values with B (all doses) were significantly greater than with P.(ABSTRACT TRUNCATED AT 250 WORDS)