When neonatally thymectomized CBA mice were implanted at 9 to 12 days of age with Millipore diffusion chambers (pore size, 0.1 micro) containing either syngeneic or allogeneic neonatal thymus, they were subsequently found to have the capacity to reject skin homografts and to form antibodies to sheep erythrocytes. In spite of displaying restored immune reactivity, thymectomized mice bearing thym...