The HandiHaler is a dry powder breath activated inhaler system developed for inhalation therapy for patients with airway disease. Its operation is based on the evacuation of powder from a pierced capsule. We sought to document the inspiratory flow rates attained by patients inspiring through the HandiHaler with various degrees of airflow limitation. Subjects with stable chronic obstructive pulmonary disease (COPD) were the study's population. An in vitro study of fine particle dose was conducted using an Andersen Cascade Impactor to assess medication delivery at low inspiratory flow rates. Subsequently, an in vivo study was conducted to determine inspiratory flow rates in patients with COPD as measured through a pneumotach with a custom coupler device with and without the HandiHaler. Patients were classified into three approximately equal groups of spirometric severity ranging from mild (46-65% predicted normal forced expiratory volume in 1 sec [FEV1]), to moderate (28-45%) to severe (< or = 27%). The in vitro study indicated delivery of medication at flow rates as low as 20 L/min. Twenty-six men completed the in vivo study (age 66.9 +/- 10.9 years, FEV1 = 1.02 +/- 0.45 l.). The median peak inspiratory flow rates attained in the mild (n = 8), moderate (n = 10), and severe (n = 8) categories were 45, 45.6, and 35.4 L/min respectively. The minimum peak inspiratory flow rates in the three groups were 28.2, 21.6 and 20.4 L/min. The HandiHaler device effectively delivers particles to the lung over a wide range of airflow limitation in patients with COPD.