Although radiotherapy is often used to treat laryngeal carcinoma, there is little information on the effects of this treatment on laryngeal structures. Rats were irradiated to the head and neck region and the larynges were studied by light- and electron-microscopy and immunohistochemistry. Ten days after irradiation, a change in the ultrastructural appearance of the granules of the subglottic glands was observed. Substance P-, bombesin- and enkephalin-like immunoreactivity was increased in local ganglionic cells and glandular nerve fibres. The mast cells were reduced in number. At examination 4 6 months after irradiation, there were no obvious differences compared with controls concerning mast-cell numbers and neuropeptide expression. The ultrastructural changes seen in the subglottic glands remained to some extent. The results show that structural changes in the subglottic glands occur concomitantly with an increased expression of certain neuropeptides in the innervation of these glands, which implies a relationship between these two parameters. The mast cells respond drastically to irradiation, but in the long run, regeneration of these cells occurs.