We studied the effect of regular inhalations of low-dose and high-dose fenoterol and low-dose and high-dose combinations of fenoterol and ipratropium bromide in maintenance treatment of 120 adults with moderately severe asthma. We used a double-blind, randomized, parallel group design comparing 12 weeks of treatment with four regimens: fenoterol, 100 micrograms/dose; fenoterol, 200 micrograms/dose; fenoterol, 50 micrograms; and ipratropium, 20 micrograms/dose in a single inhaler (Berodual) and fenoterol, 100 micrograms and ipratropium, 40 micrograms/dose in a single inhaler (Duovent). During the baseline and active treatment period the patients recorded PEFR in the morning and evening, symptoms and use of a rescue inhaler. Changes in twice daily peak expiratory flow rates or asthma symptoms did not show any significant differences among the four treatment regimens during the 12 weeks compared with the baseline period. Use of the rescue inhaler did not differ among the four groups during the active treatment. The patients' assessment of the efficacy of the active treatment favored the low-dose fenoterol and low-dose combination. More side effects were recorded in the high-dose combination group during the first 4 weeks compared with the other groups. We conclude that in maintenance therapy of chronic asthma high doses of fenoterol alone or in combination with ipratropium bromide offer no clinical advantage over low doses. On the contrary, the low-dose fenoterol and the low-dose combination are better accepted and tolerated by the patients.