IT is now a well established fact that cigarette smoke contains many noncarcinogenic and carcinogenic hydrocarbons (Cooper and Lindsey, 1955). In previous work the direct effects of several carcinogenic hydrocarbons and of cigarette smoke condensates have been studied in two organs of the respiratory tract, grown in organ culture. Benzopyrene and condensates from cigarette smoke cause hyperplasia with pleomorphism of the newly formed cells in the bronchial epitheliuin of human foetal lung (Lasnitzki 1956, 1958) and benzopyrene, methycholanthrene and DMBA induce similar changes in rat tracheal epithelium (Crocker, Nielsen and Lasnitzki, 1965). Recently, it has become possible to concentrate the hydrocarbons in the cigarette smoke condensate (Whitehead, personal communication) and the action of this particular fraction has been examined in organ cultures of human foetal lung (Lasnitzki, 1968); it produces extensive basal cell hyperplasia with atypical cytological changes in all treated explants. In experiments in vivo smoke or smoke condensates are being tested on rodents
