Transcatheter coil embolization (according to the method of Gianturco) was performed in 18 patients. It resulted in prompt and permanent occlusion of the renal artery without considerable effort and with acceptable risk. The favourable benefit of this procedure is technical facilitation of tumornephrectomy, cutting down the time of surgery, reducing intraoperative hemorrhage and danger of venous displacement of tumor-cells. The same favourable results will not be achieved by preoperative short-time radiation. Preoperative long-term radiation delays the necessary tumor-nephrectomy. Arterial embolization is preferred because it offers the wanted benefits of sufficient radiotherapy avoiding its disadvantages.