A Phase IV, 4-week, open, randomized multicenter parallel group trial compared correct use and acceptability of Diskus, Turbuhaler, and Easyhaler powder inhalers among 326 inhaler naive asthmatics/symptomatics. The subjects were asked to read the instruction leaflet before taking one dose at the first visit. The correct use was evaluated when the subject took the dose. After that, the subjects were instructed in correct use. The use of the devices was also videotaped at every visit, and independent referees judged correct use. Acceptability was evaluated by a questionnaire. At the first visit, the proportions of subjects who used the devices correctly were as follows: Easyhaler, 45%; Diskus, 43%; and Turbuhaler, 51%. The corresponding figures at the last visit were 84%, 89%, and 81%. The differences at any visit were not statistically significant. Acceptability was greater for Easyhaler and Diskus for three of eight items throughout the study, all pertaining to receiving the powder from the device and control of the inhalation of the powder. Patient education in the use of devices is important, because only half of the subjects used the devices correctly, and still after 4 weeks 10-20% could not use the devices satisfactorily, regardless of which device.