SUMMARYLymph node and spleen cells from AS rats bearing enhanced (August X AS)Fi kidneys were tested for their capacity to produce a local graft-versus-host reaction (GVHR), using the Elkins' technique and the popliteal lymph node assay. It was found that lymphoid cells from rats bearing enhanced kidneys were able to mount GVHR quantitatively similar to those caused by cells from control rats. Immunisation of rats bearing enhanced kidneys with August spleen cells caused a rise in cytotoxic antibody titre but had no effect on blood urea levels. Lymphoid cells taken from these additionally immunised rats also produced GVHR comparable with those of controls. It is concluded that tolerance is not involved in the prolonged survival of these grafts.