Bovine articular cartilage was used to examine the binding of cationized antibodies, antigens, and immune complexes to articular cartilage by charge-charge interactions. Rabbit antibodies to human serum albumin (anti-HSA) and HSA were cationized to various degrees by the addition of amino groups. When approximately 20 or more new amino groups were added to HSA and approximately 25 or more amino groups were added to anti-HSA, the proteins readily bound to cartilage and penetrated into the matrix. Soluble immune complexes made with the cationic antibodies, including small-latticed complexes, bound only to the surface of the cartilage. When cationic HSA was bound to the matrix of the cartilage, unaltered antibodies bound only to the antigen at the surface and did not penetrate the matrix. This model system defines the manner in which cationic antigens and antibodies bind to and penetrate into the articular cartilage.