When 3 mg of cationized human IgG (clgG, pI > 9) was injected intravenously into mice and followed 15 min later by 3 mg anionized bovine serum albumin (aBSA, pI = 4), deposits were detected along the capillary loops and in the mesangium. Additional infusion of immunoaffinity-purified rabbit anti-BSA antibodies 1 h later led to their deposition at the same location. Intravenous injection of an equivalent amount of preformed BSA-anti-BSA or aBSA-anti-BSA immune complexes into mice with glomerular planted clgG gave rise to few deposits. Similarly, the perfusion of preformed aBSA-anti-BSA complexes in isolated rat kidneys with planted clgG led to granular deposition of both, but the intensity of staining was less than when sequential perfusions were used. Cationic macromolecules bound to the glomerulus may lead to the deposition of anionic macromolecules and anionic immune complexes.