Objectives: 1. Investigations into pulmonary carcinogenesis with tobacco products and other potential pulmonary carcinogens for man. 2. Investigations into the factors affecting development of mesotheliomas experimentally induced with asbestos, fibrous glass, and related fibrous minerals. Major findings: Analysis of a series of 17 experiments with 17 different size distributions less than 2.5 millimicrons and lengths greater than 64 millimicrons. Work is progressing to evaluate the impact of submicroscopic fibers on this response. Several other facts have become evident during the year which require final evaluation. These include: 1) Asbestos has been established as carcinogenic in the peritoneal and subcutaneous tissues of the rat. 2) Both asbestos and ultrafine fibrous glass have been established as carcinogens for the pleura of the mouse. 3) A variety of other fibers have proven to be carcinogenic on the pleura of the rat. These include tremolite, fibrous talc, potassium titanate fibers, sodium-aluminum carbonate fibers, fibrous gypsum and fibrous silicon carbide. All of these compounds have dimensional characteristics which fit into the concept recently developed concerning the relation of structure to carcinogenicity. Proposed course: A large-scale contract, funded by DCCP, has been undertaken to test the screening ability of the pulmonary pellet method to detect differences between cigarette smoke condensate from cigarettes with high and low nicotine content.