The authors compared the histologic changes in 12 kidneys removed due to renal carcinoma with the changes in 12 other kidneys in which before nephrectomy an embolization of the renal artery with Spongostan had been performed. The results achieved show that the embolization of the renal artery may intensify the lymphocytic macrophagal and fibroplastic interstice of the tumour and according to this may represent a factor which is able to activate the cellular effector mechanism of the antineoplastic immunity of the organism.