Particulate hexavalent chromium (Cr(VI)) is a well-established human lung carcinogen with widespread exposure among people in occupational settings and the general public. However, no studies have examined the chromate-induced malignant transformation of human lung epithelial cells, its predominant target. Human papillomavirus-immortalized human bronchial epithelial (BEP2D) cells were used to better understand the mechanisms involved in human bronchial carcinogenesis induced by particulate chromate. We found that aneuploid cells increased in a concentration-dependent manner after chronic exposure to lead chromate. Moreover, chronic exposure to lead chromate induced BEP2D cell transformation. Transformed BEP2D cells developed through a series of sequential steps, including altered cell morphology, loss of cell contact inhibition and anchorage-independent growth. Specifically, a 5-day exposure to lead chromate induced foci formation with 0, 1, 5, and 10 microg/cm2 lead chromate inducing 0, 7, 3, and 15 foci in 10 dishes. Anchorage independence was observed in cell lines derived from these foci. These foci-derived cells also showed centrosome amplification and increases in aneuploid metaphases. Our study demonstrates that particulate Cr(VI) is able to transform human bronchial epithelial cells, and that chromosome instability may play an important role in particulate Cr(VI)-induced neoplastic transformation.