The adoption of a six-fraction regime of radiotherapy for patients with locally advanced carcinoma of the bronchus was followed by the appearance of radiation myelitis in eight cases. These were among a group of 130 patients given radiotherapy with anterior and posterior treatment fields, without shielding of the spinal cord. Radiation myelitis was found only in those where the calculated spinal-cord dose exceeded 3350 cGy (rad). The possible precipitating factors in the eight patients who suffered myelopathy were compared with those in the remaining 62 patients who also received spinal-cord doses calculated to be greater than 3350 cGy (rad). Only one difference was found--the haemoglobin concentration was significantly higher in those who suffered neuropathy compared with those who did not (P = 0.05).