The relationship between age and bronchodilator responsiveness (BDR) in children has not been studied using objective parameters. The aim of this study was to seek such a relationship in young asthmatic children using dose-response curves (DRC). Fourteen asthmatic subjects (age 3-9 years) with a forced expiratory volume in 1 sec (FEV1) less than 80% predicted were studied after being trained to use a spirometer reliably. Each subject completed a DRC by inhaling 5 doses of salbutamol (albuterol) at 15 min intervals until a cumulative total of 6.84 mg of salbutamol had been administered. FEV1, forced vital capacity (FVC), and forced expiratory flow at mid vital capacity (FEF25-75) were measured before and after each nebulization. In addition, arterial oxygen saturation (Sa(O2)) and heart rate (HR) were measured in some of the subjects. All lung function parameters, Sa(O2) and HR increased significantly between baseline and completion of the DRC. A significant age effect on BDR was detected in FEV1 and FVC, with older children showing a greater response than young ones. The response had plateaued after the maximum dose in the younger but not in the older children. These findings suggest that the level of response to a bronchodilator increases significantly with increasing age in young asthmatics.