The effect of preoperative irradiation on the survival of patients with renal adenocarcinoma was studied in a clinical trial. 88 patients with verified renal carcinoma entered the trial during 1968-1972, of whom 38, selected in a randomized fashion, received preoperative irradiation to a total dose of 3 300 rads in 3 weeks, followed by extrafascial nephrectomy after a 3 week interval; in the remainder an extrafascial nephrectomy was performed immediately. Actuarial 5-year survival was 47% in the "preoperative irradiation" group and 63% in the "nephrectomy-only" group, i.e. preoperative irradiation did not improve the 5-year prognosis. Survival was also studied in P-categories of the U.I.C.C. as well as in high and low grade malignancies. In none of these groups could we find a clear tendency to a more favourable prognosis with preoperative irradiation; no statistically significant differences were found. Because no improvement in prognosis after preoperative irradiation was found in our series or any of the sub-groups, we consider preoperative irradiation not routinely indicated as an adjuvant therapy. It may be useful in some selected cases, but selecting these cases will be difficult.