The budesonide dose delivered to the patient from three different spacer devices (Nebuhaler=750 ml, Aerochamber=140 ml, and Babyspacer=260 mi) was assessed by measuring the budesonide dose deposited on a filter inserted between the spacer outlet and the mouth of the patient. Twenty children aged 10-25 months were given a single dose of 200 mu g budesonide from each spacer device in a randomised crossover study. Ah spacers had a facemask attached and a one way valve system. The children breathed through the inhalation system for 30 seconds. Furthermore, the minute ventilation of the children through a tightly fitting facemask was measured. The filter dose of budesonide was significantly lower after Aerochamber treatment (39.4 mu g, range 19-67 mu g) than after Nebuhaler (53.5 mu g, range 34-88 mu g) and Babyspacer (55.5 mu g, range 39-76 mu g) treatment. The minute ventilation of the children varied from 1.4 l/min to 7.0 l/min (mean 5.0 l/min). This was sufficient to empty all spacers within the 30 seconds of inhalation. It is concluded that spacer volume does not seem to be so important for children aged 10-25 months as long as spacers with a volume lower than 750 ml are used.