The effect on nebuliser output of varying the flow rate of compressed air driving the device and the volume of respirator solution used was investigated in four brands of jet nebuliser. Raising the airflow rate from 4 to 6 1/min reduced the duration of nebulisation by approximately 40%, and a rise from 6 to 8 1/min reduced the duration by a further 15%. However, this change had only a slight effect on the proportion of the solution released. The volume of respirator solution placed in the nebuliser directly influenced the volume released as aerosol. After a 2 ml fill, less than 1 ml was released (50%). With a volume fill of 4 mg 60-80% was released, and with 6 ml 70-85% was released. Nebuliser output fell during nebulisation as the temperature of the solution dropped by 8-12 degrees C. A minimum 4 ml fill and an air-flow rate of 6 l/min are advocated to optimise nebuliser output.