Damage to bowel often complicates radiotherapy for abdominal and pelvic malignancy. The symptoms of chronic irradiation enteropathy, which often include intractable diarrhoea, are generally attributed to vascular injury. We have examined specimens of bowel resected from patients who had been therapeutically irradiated to assess the extent of injury to the enteric nerve plexuses. To facilitate visualisation of nerve fibres and cells of neural or neuroendocrine origin, sections were immunostained with antibodies to neuron-specific enolase or PGP 9.5, widely used markers of nerves and neurons. Electron microscopy was performed in selected cases. In 27 out of 33 specimens the number of nerve fibres in the lamina propria was obviously increased compared to that in control material. Scattered cells with the histological, immunohistochemical and ultrastructural features of ganglion cells were noted within the lamina propria in 23 of the specimens, and in 18 cases so-called neuroendocrine cells, not normally seen in this location, were also present. These radiation-induced changes in the innervation of the bowel may contribute to the symptoms of chronic radiation enteropathy.