[en] In animal studies concerned with the deposition of particulate matter in the lung, two methods for delivery of particles are commonly used, aerosol inhalation and intratracheal instillation of particle suspensions. We have attempted to evaluate the distribution patterns of each of these methods. Particles labeled with /sup 99m/Tc were administered to both rats and hamsters. The animals were subsequently killed. The lungs were excised, weighed, inflated, dried, and divided into 54 pieces which were counted individually in a Nuclear-Chicago Model 4230 Automatic Gamma Scintillation System. Groups receiving intratracheal instillations demonstrated nonuniform distribution patterns with preferential deposition in the dependent portions of the lung. The aerosol groups evidence more even distribution with preferential deposition in the apical lobes