We studied the frequency of malfunction, variability in rate of nebulization, and effect of this variability on aerosol particle size of eight disposable jet nebulizer models produced by six manufacturers. Four of eight models showed visual signs of malfunction, including spraying of large, individually visible droplets, leaking of nebulizer solution, and air leaks that completely prevented nebulization. Variability of nebulization rate within specific models ranged from 57 to 129 percent. The model with the largest variability of nebulization rate was also associated with an unacceptably large variability in particle size. In contrast, two models with smaller variability in nebulization rate had greater consistency of particle size. These results indicate poor quality control by some manufacturers in the disposable nebulizer industry. The data suggest that purchasing agents should consider reliability as well as cost before selecting a specific nebulizer model and that their evaluation should include physical testing of multiple units of each model under consideration.