This study investigated the influence of the use of different types of inhalers on the adequacy of inhalation technique among adult asthmatics. Three hypotheses were tested: first, patients using only one type of inhaler will demonstrate adequate inhalation technique more often than those with two or more types. Secondly, patients using a combination of dry powder inhalers (DPIs) will demonstrate correct inhalation technique more often than those using the combination of a metered dose inhaler (MDI) and a DPI. Thirdly, some inhalers or combinations of inhalers are more prone to erroneous inhalation technique than others. Adult outpatients with asthma who regularly used inhaled steroid therapy (n=321) participated in the study. The inhalers investigated were MDIs on the one hand, and the DPIs Turbuhaler, Diskhaler, Cyclohaler, Inhaler Ingelheim and Rotahaler on the other. Of 208 adult asthmatics with only one inhaler, 71% made no inhalation errors versus 61% of 113 patients with two or more different inhalers. Of patients with a combination of DPIs 68% performed all essential checklist items correctly, versus 54% of patients with the combination of "regular" MDI and DPI. Patients using only the Diskhaler made fewest errors. Whenever possible, only one type of inhaler should be prescribed. If a combination is unavoidable, combinations of DPIs are preferable to MDI and DPI. The Diskhaler seems to be the most foolproof device.