The results of the treatment of 762 cases of malignant disease with X-rays generated at one million volts are presented. Patients referred for million-volt therapy were incurable by any other means, either because of the nature of the tumor, its anatomical extent or the general condition of the patient. The scope of radiotherapy as a palliative agent is stressed. It was found that tumors that respond poorly to ordinary X-ray therapy show no marked differences in response to million-volt therapy, with the possible exception of carcinomas of the rectum, bladder, antrum and larynx. No evidence of any biological difference in response due to the shorter wave length was found. Any improvement in results was felt to be due to ease of appln.