Asthma is characterized by variable airflow obstruction, hyperresponsiveness of airways to endogenous or exogenous stimuli and inflammation. Inadequacy of the techniques to use different inhalation devices is a cause of no response to treatment. The main purpose of this study was to evaluate how 20 medical students, 36 resident physicians on Internal Medicine/Pediatrics, and 40 asthma patients used three devices for inhalation therapy containing placebo. All patients were followed at the Pulmonary Outpatient Service of Botucatu Medical School and had been using inhaled medication during the last six months. The following devices were evaluated: metered dose inhalers (MDI), dry powder inhalers (DPI), and MDI attached to a spacer device. A single observer applied a protocol containing the main steps necessary to obtain a good inhaler technique to follow and grade the use of different devices. Health care professionals tested all three devices and patients tested only the device being used on their management. MDI was the device best known by doctors and patients. MDI use was associated with errors related to the coordination between inspiration and device activation. Failure do exhale completely before inhalation of the powder was the more frequent error observed with DPI use. In summary, patients have not been receiving repeated instruction on how to use inhaled medication and health care professionals are not well prepared to adequately teach their patients.