The pulmonary effects of chronic marijuana (M) and tobacco (T) smoke inhalation were studied in adult female dogs. The smoke was inhaled through a tracheostomy tube: four cigarettes containing either tobacco (3.2 g/dog) or marijuana (3.0 g/dog) were used per day over 900 days. At autopsy, the pulmonary volume and alveolar surface of the T group had decreased, compared to controls (C) and the M group. The tracheostomy (Tr) produced itself result in chiolitis; in order of severity the M group greater than T greater than Tr greater than C. The incidence of squamous metaplasia also followed this order but the T group showed more abnormalities affecting the mucosal membrane. Our findings reported that chronic inhalation of marijuana and tobacco produced the bronchiolitis with the macrophage infiltration in the wall of the terminal air-passages. This may thereafter induce the pulmonary emphysema.