Grafts of intact cartilage tissue and cell suspensions of chondrocytes enzymically freed from the surrounding matrix have been placed in isogenic strains of rats. When intact cartilage allografis were placed in a nonsensitized host, they showed no evidence of resorption, but similar allografts placed in presensitized hosts were surrounded by a peripheral infiltrate of predominantly lymphocytic host cells. Suspensions of allogeneic chondrocytcs reformed cartilage after inoculation into the tip of the tongue of both presensitized and nonsensitized hosts but, in both instances, the grafts were followed by peripheral infiltrates of host mononuclear cells. It is concluded that 1he matrix around the: chondrocytes prevents the rejection of allografts of intact cartilage placed in nonsensitized hosts, and that the privilege afforded such grafts is not a result of the lack of antigenicity of the cells.