In 7 dogs renal arterial embolization was performed using the Seldinger technique and an inflatable Swan Ganz balloon catheter. Methyl methacrylate and butyl-2-cyanoacrylate were injected. 6 months later, the tissue concentration of Cefazolin was measured in the embolized and contralateral kidneys and in serum 2 h after a short infusion of 1 h Cefazolin. The concentrations in serum and homogenized kidney tissue were determined by means of the agar gel diffusion method. Angiography showed no vessels in the embolized kidneys. Histologically there was total atrophy of the tissue, especially of the tubular system. The mean tissue level of Cefazolin in the embolized kidney was 70% of serum. The tissue concentration was always above 10 micrograms/g. This concentration is high enough to inhibit nearly all strains of E. coli, Klebsiella, Salmonella, Shigella and a large part of Proteus mirabilis, whereas nearly all gram-positive bacteria are inhibited at a lower concentration. The value and necessity of antibiotic therapy in embolized kidney cancer is discussed.