A macromolecular component has been identified in the rat lung which binds the chemical carcinogen, 3-methylcholanthrene. At the present time, only a preliminary characterization of this component has been achieved. Its most striking property is that it has been found only in the lung. The present research proposal is designed to provide a complete physicochemical characterization of the binding component. In addition, several approaches will be used to establish its biological significance. These will include: (1) analysis of the specificity of this component in binding a variety of compounds and the relation of this data to carcinogenic potencies; (2) studies of the dynamics of carcinogen binding in the lung using in vivo and tissue incubation systems; (3) a comparison of binding activity in normal and cancerous lung tissue; and (4) investigations of the effects of developmental or hormonal factors in modulating binding activity in the lung.