Lung injury and inflammation are associated with exposure to various types of particulate air pollutants. The present study was used to determine whether metalloproteinases (MMPs) are secreted after instilling dust samples into the lung, and to relate levels of specific MMPs to different fractions of the ambient air particle sample EHC-93. Rats received an intratracheal injection of 5 mg dust samples in 0.5 ml water and were killed at intervals from 4 hours to 28 days later particle samples were EHC-93 whole dust, and the insoluble, leached, and soluble fractions of the same dust. Samples prepared from EHC-2K dust were also used, as were solutions of zinc and copper chloride. All samples induced inflammation as measured by increased inflammatory cells in bronchoalveolar lavage (BAL) fluid; the highest levels were found 1 to 3 days after instilling the whole dust. This dust also induced production of MMP-2 and MMP-9 as shown in zymograms. The leached dust induced predominantly MMP-9, which was maximal at 4 hours and 1 day. In contrast, the soluble fraction induced almost exclusive 4 MMP-2, also maximal at 4 hours and 1 day; this enzyme was also produced in response to soluble zinc, the most prevalent soluble metal in the EHC samples. The results demonstrate the rapid production and secretion of MMPs in the lung after particle deposition. A differential pattern of MMP production is seen with MMP-9, likely from inflammatory cells, being produced in response to the insoluble particles, and MMP-2, likey from epithelial cells, being produced in response to the water-soluble fraction of the atmospheric dust.