“…Indications that B and T lymphocytes reactive against the same antigenic deternninants express shared idiotypic determinants on their respective antigen-binding receptors stem from several sets of observations (3, 5-14, 17, 18, 24, 29, 31-36). In the present article we will primarily dis-cuss two systems: in the rat using the major histocompatibility Ag-B antigenic determinants as the immunogen (2-6, 8-12, 19, 29) and in the mouse using the group A streptococcal carbohydrate as the antigenic determinant (17, 18), It should, however, be realized that important pioneering work using the anti-receptor approach has been carried out in the mouse using H-2 or minor transplantation antigens as target structures (7,13,24,26,(31)(32)(33)(34)(35)(36), reaching conclusions very similar to those made in the presently discussed systems. In the rat system, using the principle design of Ramseier & Lindenmann for the mouse (31), it was first shown (2-6) that Fj hybrids between two inbred strains will synthesize anti-alloantibodies if inoculated with parental lymphocytes or alloantiserum produced in the same parental strain against the alloantigens of the other parental strain.…”