Two hundred and fifty eight adult patients with bronchial asthma participated in an open, parallel group study of 8 wks duration. During a 2 wk run-in period the beta 2-agonist terbutaline (0.5 mg q.i.d) was delivered via a pressurized freon aerosol, Bricanyl metered dose inhaler (MDI). During the following 6 wks, one third of the patients continued with MDI and two thirds with the same dose of terbutaline in the form of dry powder, Bricanyl Turbuhaler. There were no statistically significant differences in the increases in peak expiratory flow rate (PEFR) after inhalation between the two treatment groups. The asthma symptom scores decreased in the Turbuhaler group during the study but remained the same in the MDI group. No difference in use of extra trial medication during the day was found. During the night, the difference was statistically significant in favour of Turbuhaler (p less than 0.05). Turbuhaler was well accepted and easy to use. As compared with the MDI used during run-in, 50% of the patients in the Turbuhaler group preferred to use Turbuhaler and 26% MDI, whilst 24% had no preference. In conclusion, Turbuhaler was at least as effective as MDI during the whole Turbuhaler life-span (6 wks).