One of the newest approaches of toxicology is risk assessment, whereby scientific information on the hazardous properties of toxic agents and the extent of exposure results in a statement as to the probability that exposed populations will be effected. This process is a scientific attempt to identify and estimate the true risks). Significant exposure-response relationship has been reported for both lung cancer and asbestosis. The cumulative exposure relation for lung cancer was reported to be linear on a multiplicative scale. Excess lifetime risk at permissible exposure level of Chrysotile (0.1 fiber/ml), was predicted to be about 5/1,000 for lung cancer, and 2/1,000 for asbestosis).