An increasing amount of experimental data has been accumulating which indicates clearly that the intestinal epithelium is peculiarly sensitive to the hard roentgen rays that are used so much in modern therapy. In the light of this knowledge, we wish to review some of the scattered and incomplete observations in human cases, as we believe the evidence is convincing that the intestinal epithelium in man is likewise sensitive to the hard or short wave length roentgen rays. If this is an established fact, we must use care in the exhibition of roentgen rays when the small intestine is exposed to irradiation; for example, in the treatment of pelvic tumors. There can be little doubt that the small intestine can be injured by roentgen-ray therapy in human beings, and it is certain that any such injury is serious. We know that roentgen-ray skin "burns" or "ulcers" are very chronic, and we