The embolization of tumors in the treatment of hypernephromas is discussed on the basis of 13 cases. The method involved the use of three different substances: thrombin (Topostasin), homogenized muscle pulp, and fibrin from the patients own body, 600 units of thrombin being subsequently injected. In each case the embolization material was introduced into the tumorous kidney via an indwelling terminally open Kifa catheter after preoperative selective angiography. A differentiation is made in the indication between prophylactic embolization, which is performed preoperatively to prevent extensive hemorrhaging and increased tumor cell dissemination, and curative embolization applied in the case of patients presenting a greatly increased operation risk, inoperable tumor, or large-scale hematuria. The paper discusses the course of the treatment, possible complications, and postembolization in terms of case histories. The fibrin-thrombin method, beause of the small expenditure of time and technical resources involved, presently appears to be most favorable form of renal tumor embolization. Other methods are discussed on the basis of the literature.