[en] Local control of primary and recurrent tumors after irradiation of fourth-generation transplants of mammary carcinoma, MDAH-mCa-4, in C₃H mice was studied using single and 5 fractionated exposure to gamma rays in hypoxic conditions. No significant difference in dose required to produce local control in 50% of each group (TCD 50/120) was observed between the primary tumors and the recurrent tumors. The results indicate that the average dose recovered per fraction interval (when each fraction was about 2,000 rads) was 880 and 840 rads for the primary and for the recurrent tumors, respectively. (auth.)