The study was undertaken to evalute the radioprotective effects of angiotensin on gastrointestinal tract. Atotal of 314 mice were used for the experiment, of which 264mice were used to assess the effect of angiotensin onresponse of gastrointestinal tract to irradiation, and 50 mice to assess relative blood volume decrease withangiotensin of the intenstine, which was resected immediately after whole blood volume was measured. For theassessment of effects of angiotensin on gastrointestinal tract to irradiation, graded doses of 800,1000,1200, and1400 rads were irradiated to the whole body of the control and angiotensin-treated animals in which most probablemechanism is the hypoxia due to decreased intestinal blood volume.