The carcinogenic activity of different types of asbestos of the USSR was investigated. All samples of chrysotile had traces of benzo[a]pyrene (BP). Chrysotile asbestos had a high adsorption activity. BP was not found in anthophyllite and magnesiaarfvedsonite. Intratracheal injections and inhalations of different kinds of chrysotile induced pulmonary carcinomas, sarcomas, and precancerous lesions in rats. The number of such lesions was higher if asbestos and BP were introduced together. Intrapleural administration of chrysotile asbestos induced several types of mesothelioma and premesotheliomatous lesions in rats. A transplantable mesothelioma (MSh-71) is in its twenty-sixth generation.