We investigated compliance and inhaler technique in 50 patients with airway obstruction (26 asthma, 24 chronic bronchitis) being treated with inhaled steroid (beclomethasone dipropionate, BDP) via a dry powder inhaler (Rotahaler omega). Patients had already participated for one year in a 2-year trial of BDP in general practice. They were treated daily with two dry powder inhalations of 400 micrograms BDP in combination with a bronchodilator. Compliance with BDP was measured by counting capsules (single-blind) at the end of a 4-month period and through a questionnaire. Counting capsules revealed non-compliance in 46% of the patients. Compliance was not related to age, sex, diagnosis or side-effects of BDP. In chronic bronchitis, but not in asthma, compliance was related to the outcome parameters of steroid treatment (pulmonary symptoms, change in lung function and non-specific bronchial responsiveness). The inhaler technique was judged insufficient in 27% of the patients. This study stresses the importance of regular instruction in inhaler technique and proper information about prophylactic steroid treatment by the general practitioner during the treatment of asthma and chronic bronchitis.