We believe it can be concluded that acute hypoxia has a radioprotective effect on normal tissues during accelerated hypoxyradiotherapy of colorectal carcinoma. Hypoxyradiotherapy permits safe administration of doses higher than those tolerated by normoxic, noncanceorus tissue, resulting in the amplification of the biological effect of radiation on tumor tissue and contributing to an improved outcome after combined radiosurgical treatment of colorectal carcinoma.