The causal relationship between asbestos and mesothelioma has been well understood for more than 40 years. However, several critical issues continue to be debated regarding human exposures to chyrostile asbestos and the risk of developing malignant disease. We have invested more than 100 person years into studying the importance of fiber type and the relative risk of malignancy, the importance of fiber length, and the specific concentration which might be considered a “threshold dose” for both serpentine and amphibole asbestos. Our scientists have published more than a dozen articles on exposure or the health effects of asbestos.