This study was conducted to determine whether small doses of salbutamol solution, aerosolised and delivered by intermittent positive-pressure breathing (IPPB), would be as effective as the 5 to 10 mg dose usually recommended for inhalational use. In nine asthmatic subjects we found that there was no significant difference between the peak bronchodilator effect of 1.0, 2.5, and 5.0 mg of salbutamol solution as assessed by FEV1 (P greater than 0.05). The 5 mg dose of salbutamol solution caused a significantly longer duration of effect than the 1.0 mg and smaller doses of salbutamol, but it also caused four of the nine subjects to complain of unwanted effects. In addition, a radiotracer technique in four normal subjects showed that an inverse relationship exists between the amount of aerosol deposited in the lungs and the tidal folume of IPPB. The maximum dose deposited in the lungs was about 10% of that initially present in the nebuliser.