SUMMARY Auto- and allogeneic chondrocytes isolated from septal cartilage by enzymic digestion were transplanted into rabbits together with intact fragments of the same cartilage. In other animals fragments only of cartilage were grafted. Cartilage formed by autogeneic chondrocytes was devoid of infiltration, whereas that formed by allogeneic chondrocytes was mostly surrounded by massive infiltration, composed predominantly of lymphocytes and plasma cells. Resorption of such cartilage was also found. Auto- and allogeneic fragments transplanted alone did not evoke infiltrations. When similar fragments were transplanted together with isolated chondrocytes, infiltrations were frequently formed in the vicinity of the allogeneic fragment. It is concluded that isolated allogeneic chondrocytes evoke immunization and may perhaps sensitize the animals against allogeneic fragments of cartilage.