A prototype high-frequency ultrasonic nebulizer, coupled with a nebulization chamber, has been designed specifically to overcome the problem of inefficient and unpredictable radioaerosol delivery. The objective was to reduce mean particle size, increase aerosol concentration, and minimize dead space. Thirty-nine patients were studied, including 15 patients in significant respiratory distress. Delivery of the radioaerosol proved to be rapid, efficient, and reproducible, and excellent alveolar distribution patterns were obtained in all 39 patients. Minimal nonpathologic tracheal deposition occurred in five patients, but this did not interfere with the interpretability or diagnostic validity of the study. All other instances of airway aerosol deposition correlated with documented airway disease. The images obtained with this system are a reliable measure of ventilatory distribution and airway tubulence.