We propose to explore factors and events involved in asbestos carcinogenesis. Asbestos fibers incorporated in Ivalon-sponges will be inoculated into the pleural spaces of mice as well as intraperitoneally and subcutaneously. The carcinogenic process will be followed and analyzed, employing a methodology previously developed for the study of foreign body tumorigenesis. Specifically, the following questions regarding asbestos carcinogenesis will be investigated: Cell type of tumor origin; frequency of preneoplastic foci; morphological and cultural characteristics of preneoplastic cells; their mono- or pluriclonal origination and expansion; pre-neoplastic kinetics and maturation stages at the tissue and cellular levels; timing and nature of physical interaction between asbestos fibers and cells at various defined stages of the carcinogenic process; the role of tissue fibrosis and phagocytic macrophage activity. In view of the fact that asbestos and other tumorigenic fibers cannot easily by eliminated from the environment of an industrial society, we need a deeper and detailed understanding of the carcinogenic process in asbestosis if we want to approach prevention and cure by different and additional means.