Since 1967 we have been using preoperative radiation therapy for renal cell carcinoma as proposed by Riches. Radiation therapy, to include the para-aortic lymph nodes, is given in 250-rad increments four times weekly to a total dose of 3,000 rads. After an interval of three weeks following radiation therapy, we performed radical nephrectomy. The object of this preoperative treatment is devitalization of growing cells in the periphery of the tumor, thus preventing metastases and local recurrence, and and decreasing the size of the tumor and thereby facilitating surgery. In one third of the cases there is radiologically demonstrable decrease in the size of the tumor, probably secondary to obliteration of the dilated veins in the capsule. The delay of six weeks has had no adverse effect on the outcome of metastases.