A compressed-air nebulizer with low holdup and high output was used to nebulize [99mTc] pertechnetate presented in normal saline. Generated droplets were dried in line and led to an inhalation chamber from which the dry aerosol was inhaled using a nose or mouth inhalation unit. The mass median diameter of the particles was 0.8 microns, with an associated geometric standard deviation of 2.0. The deep lung delivery efficiency--defined as the ratio of the activity deposited in the lung area to the activity nebulized--was found to be reproducible and consistent (15-22%) in all the subjects studied. A 3-5 min inhalation of aerosol, nebulized from 20 mCi, was sufficient to provide a lung image of good information density. No noticeable deposit was seen in the trachea or major brochi. The system is inexpensive, stable in performance, adaptable to other solutions or colloids, and is promising for routine use.