For the purpose to observe the possible vessel wall damage by deionization of the related anionic groups the perfusion test of rat kidney and aorta with cationic iron colloid particles and the injection experiments with albumin-poly-L-lysine complex were carried out. By staining the fixed tissue sections with the cationic iron colloid at pH 7.3 the ionized anionic sites on vessel walls have been demonstrated histochemically. The perfusion test of living tissue with the cationic iron colloid induced the desquamation of the endothelial cells. The perfused colloid particles were adsorbed to the whole endothelial cell surfaces facing to luminal and subluminal sides. Albumin-poly-L-lysine complex injected into vein deposited in the subendothelial spaces of glomerular capillaries through the endothelial cell layer having the well-kept anionic barriers. Discussion was made on possible damage of vessels due to the deionization of anionic groups of endothelial cells and serum proteins by general cationic molecules.