An integrated bioassay program is being developed to evaluate the toxicity of inhaled particulate materials. The multi-disciplined approach combines studies on lung clearance mechanisms with pulmonary macrophage functional assessments based on cellular biology, biochemical and cytochemical evaluations on lung specimens from exposed animals. To validate this method, animals were exposed to asbestos, iron-treated asbestos, fiberglass, Mt. St. Helens ash or carbonyl iron particles. Deposition patterns, macrophage migration and phagocytosis were monitored in vivo at selected time periods after exposure. Our results showed that chemotactic factor generation by particles in vitro correlated with the corresponding macrophage recruitment responses in vivo. In addition, macrophage morphologic and functional characteristics were evaluated following exposures to aerosolized dusts. Our results suggest that scanning electron microscopy (SEM) techniques for investigating particle deposition and macrophage clearance provide an important component for evaluating the toxicity of inhaled particulate materials.