Radiation-induced cytomorphologic atypia is presented. The cellular changes produced by radiation therapy were studied in cytologic samples from eight patients with bronchogenic carcinoma. Pulmonary specimens were obtained from sputum, and washing and brushing examination in patients before and after radiation. In all 48 samples with 213 slides were reviewed by light microscopy. An increased number of metaplastic cells and macrophages, as well as a high leukocyte concentration in post-radiation samples were observed in the majority of the patients. Nuclear and cytoplasmic vacuolization were the most frequent damage observed in the post-radiation group. The alterations of epithelial cells, which are often found in the cervix, were rarely observed in the pulmonary specimens.