The authors carried out some series of experiments under the conditions of organ cultures of lungs of mice, treated with urethane and 3,4-benzpirene. They succeeded lung culturinf up to 14-th and 21-th day. Growths of bronchial and bronciolar epithelium manifested at various degree were obtained in the lung extracts from mice, treated with urethane and 3,4-benzpirene. The most manifested proliferation was observed in extracts, treated with urethane at a dose of 10 mg/ml and 3,4-benzpirene -- 64 gamma/ml.