We have compared radioaerosol deposition pattern and bronchodilator response following inhalation of 100 micrograms of albuterol from a correctly used conventional metered dose inhaler (MDI) to those from Gentlehaler, a new compact low-velocity pressurized aerosol device (Schering Corporation), in a group of ten asthmatic patients (mean baseline FEV1 52 percent; reversibility > 15 percent). Whole lung deposition (mean 18.8 percent of dose by conventional MDI, mean 19.9 percent of dose by Gentlehaler), regional lung deposition, and bronchodilator response were similar for the two devices, but oropharyngeal deposition was halved by Gentlehaler. The spray velocity from Gentlehaler was less than 2 m s-1 compared with a velocity of greater than 30 m s-1 commonly found in the conventional device. Gentlehaler may therefore play a valuable role in inhalation therapy, notably by reducing "cold Freon" problems (respiratory inhibition) in pressurized aerosol delivery, and by reducing oropharyngeal losses of inhaled corticosteroids.