A study was carried out in 8 patients with chronic stable bronchial asthma to compare the bronchodilator response with terbutaline, administered by a recently developed powder inhalation system ('Turbuhaler') and equipotent doses of salbutamol administered by a widely used powder inhaler ('Rotahaler'). Dose-effect relationships with usually applied clinical doses of the bronchodilators were estimated by maximal expiratory flow-volume analysis and airway resistance estimates from body plethysmography. There was no significant difference in clinical response using either inhaler. The equal and opposite changes in forced vital capacity and residual volume with increasing dose indicate an improvement in peripheral airway resistance and, therefore, adequate peripheral powder deposition of the bronchodilators. Only at the highest dose was a mild increase noted in pulse frequency and tremor score with both systems. It is suggested that, because of the multi-dose character, absence of additives, easy handling (no capsule loading) and low inspiratory flow needed for actuation, the 'Turbuhaler' system may be considered preferable for the application of a bronchodilator in children and severely obstructed adults.