Epidemiologic investigation has established an association between exposure to particulate matter (PM) and human health in the Utah Valley. Reduction of particle mass during the temporary closure of a local steel mill was associated with diminished morbidity and mortality. We tested the hypothesis that the biologic effect of PM would reflect findings of epidemiology with a greater injury after exposure to an equal mass of particles from those years in which the mill was in operation. Filters containing PM were collected prior to closure of the steel mill, during the closure, and after its reopening. Aqueous extracts of the filters were prepared. One of three extracts (500 microg) was instilled through the bronchoscope into the lungs of nonsmoking volunteers. Twenty-four hours later, the same subsegment was lavaged. Exposure to aqueous extracts of PM collected before closure and after reopening of the steel mill provoked a greater inflammatory response relative to PM extract acquired during the plant shutdown. This is the first demonstration that pulmonary effects after experimental exposure of humans to PM can correlate with health outcomes observed in epidemiologic studies of the same material under normal exposure conditions. Findings suggest that mass may not be the most appropriate metric to use in assessing health effects after PM exposure but rather specific components must be identified and assessed.