The amount of budesonide suspension actually delivered to six subjects (aged 4-30 months) by a jet nebuliser and spacer system (System 22) was determined. Two nebulisations were performed in each subject using a filter at the exhalation outlet of the inhalation chamber. An inhalation filter was additionally attached between the facemask and the spacer in the first test. The drug was inhaled during the second test. The nebuliser equipment was washed with ethanol and the amount of drug deposited was determined. The amount of budesonide deposited in the exhalation filter increased when the inhalation filter was omitted. Only 14% of the nominal dose (500 micrograms) of budesonide was found in the inhalation filter, increasing from nine to 19% with increasing age. Approximately 75% of the nominal dose was found in the nebuliser equipment. These findings must be considered when deciding the nominal dose of budesonide suspension to be given to infants and toddlers.