The protective effects of glutathione (GSH) against radiation were studied by the single, blind method in patients with carcinoma of the uterine cervix treated by radiotherapy. The background factors were same in the GSH group as in the control group. The results revealed that the occurrence of abnormal values of WBC, PLT, GOT, GPT and hematocrit in the GSH group were significantly lower than those in the control group by signed rank test, which suggests a possibility that GSH prevents these blood findings from becoming abnormal. In subjective or objective symptoms, the appearance of general lassitude was significantly reduced in the GSH group. Blood findings were studied in relation to NSD.