In the experiment using guinea pigs, the accumulated portions of IMP after 125I-IMP microautoradiography were compared in a normal control group and a group exposed to cigarette smoke. In the smoke-exposed lung, the accumulation of silver grains were observed in the alveolar spaces and alveolar macrophages, as well as in the pulmonary capillaries and the alveolar epithelia. After the broncho-alveolar lavage (BAL), increases in alveolar macrophages, total counts of BAL fluid and counts of cell components were seen in the smoke-exposed lung. These results suggested that abnormal function of the pulmonary capillary or alveolar epithelium was wide spread in the smoke-exposed lung.