It is previously well known that bombesin has effects as growth factor and that changes in bombesin content in air-way structures occur in various patho-physiological conditions. In the present study, the effects of radiotherapy on bombesin expression in the rat larynx were studied. Irradiation was given for five days, 6 or 8 gray daily. Ten days after cessation of irradiation, the subglottic part of the larynx from irradiated and control animals was dissected out, and processed for immunohistochemistry or radioimmunoassay. The radioimmunoassay analysis showed that the content of bombesin-like material increased 2-fold after irradiation. The immunohistochemical analysis displayed an increased bombesin-like immunoreactivity in local ganglionic cells and in nerve fibers in the submucosal glands. These nerve fibers are likely to be derived from the local ganglionic cells. On the other hand, there was no change in the pattern of immuno-reactivity in the innervation of the epithelium and the lamina propria, including the blood vessels. The observations show that radiotherapy can be added to the list of factors that influence bombesin expression in airway structures.