This study was conducted by the AFLM order to determine the performance characteristics of 12 commercially available nebulizers (6 ultrasonic and 6 jet) used in the treatment of cystic fibrosis (CF). The nebulizers were connected to a circuit which simulated the ventilation of a CF child and CF adult, and were tested using three drug solutions: tobramycin (T), colistin (C), and amiloride (A). Nebulizer performance was evaluated according to the volume of drug solution delivered in 10 min during the simulated inspiratory phase (VI), drug granulometry (G%), drug concentration modification in the nebulizer reservoir (delta C), and percentage of efficiently aerosolized drug EA%). The ultrasonic devices delivered a significantly higher VI than the jet nebulizers (p < 0.0001) for all three study drug. Ventilation rate did not influence VI. Regarding granulometry, higher percentages of T and A were found to be contained in droplets ranging from 0.5 to 5.0 micron following ultrasonic nebulization. Drug concentration modifications were independent of the nebulizer used but were influenced by drug type; overconcentrations of T and A were observed (delta C = +10.5 +/- 18.6 and +13.4 +/- 8.9%, respectively). On average, the ultrasonic devices achieved a higher EA% than the jet nebulizers (17.3 +/- 6.7 and 9.7 +/- 9.6%, respectively). This study highlights the significant variability in performance of different nebulizer types and empahsizes the importance of accurately testing nebulizers prior to clinical use so that the most efficacious nebulizer/drug combinations may be prescribed.