Epidemiologic evidence has helped in defining and measuring the risks of asbestos exposure. Further investigations are required to confirm the differing carcinogenicity of the various types of asbestos and related fibers. The evidence relating crocidolite asbestos to malignancy is not universally accepted. Most standards for concentrations of asbestos in the air are currently being adopted and the proposed British standard is about to be reduced to 1 fiber per milliliter for chrysotile asbestos, 0.5 fiber per milliliter for amosite and is to remain at 0.2 fiber per milliliter for crocidolite asbestos. 37 Careful prospective studies are still required in order to evaluate the efficacy of these standards in the prevention of asbestos related diseases. In addition, further epidemiologic studies are necessary to determine the relationship between asbestos exposure, particularly the low level exposure, and its potential cocarcinogenic role with other carcinogens in the evolution of the wide spectrum of human malignancy.