The two most common albuterol preparations used for nebulization are: (1) Ventolin (albuterol) respirator solution (Glaxo Canada Inc; Montreal, Canada) of which 2.5 mg (0.5 mL) is diluted with 2 mL of normal saline solution, and (2) the preservative-free, prediluted Ventolin (albuterol) Nebules PF (Glaxo) (2.5 mg/2.5 mL). The two preparations were compared using both a Hudson 1720 "T" up-draft Neb-U-Mist jet nebulizer and a Hudson 1730 "T" up-draft Neb-U-Mist II jet nebulizer (Hudson; Temecula, Calif), which were driven by a compressor (Pulmo-Aide; Devilbiss; Somerset, Pa) and by dry compressed air at 6 and 8 L/min. Particle size distribution was measured with a particle sizer (Malvern 2600; Malvern Instruments; Malvern, UK) and drug output for the nebulizer was calculated from the differences in predrug and postdrug volume and concentration. Drug availability was defined as the amount of drug carried in particles less than 5 microns in diameter. Drug availability was greater with the albuterol respiratory solution, due to the surface activity of the preservative benzalkonium chloride, for both nebulizers but particularly for the 1720. Differences in drug availability between nebulizers exceeded fourfold depending on the preparation, the nebulizer, and the nebulizing flow. These differences could not have been predicted from the manufacturer's specifications. The results suggest that prediction of drug availability must be based on measurements with the specific preparation and the specific nebulizer used.