In experimental and clinical use, Ethibloc in combination with 40% glucose preinjection has proven to be of major advantage in tumor embolization. However, its low radiographic contrast is a limiting factor in monitoring its vascular distribution and venous propagation. Various contrast media were tested in order to enhance this contrast in laboratory and animal experiments. Normal rat kidneys (N = 96) and renal tumors, induced by Dimethylnitrosamine (N = 66) were tested as in previous studies. Ethibloc-N was produced by substituting Lipiodol for poppy seed oil which is an ingredient of the original Ethibloc. This proved to be the only embolization medium that combined the excellent properties of the original Ethibloc with increased contrast. All other embolization media tested resulted in new complications such as under-or overembolization and pulmonary embolism.