Balb/c myeloma proteins, TEPC 15 and MOPC 167, bind phosphorylcholine and precipitate with the C-polysaccharide moiety of pneumococci R36A. Anti-idiotypic antibodies to TEPC 15 myeloma raised in A/He mice prevent plaque formation by cells releasing antibody to phosphorylcholine and inhibit induction of the antibody response to phosphorylcholine in vitro and in vivo. This suppression is specific since antibodies against non-crossreacting idiotypic determinants of MOPC 167 do not prevent either formation of plaques or induction of the antibody response. Furthermore, the response to sheep erythrocytes is not suppressed by antibodies to TEPC 15. These results indicate that antibodies to phosphorylcholine and cell receptors for phosphorylcholine share similar antigen-binding sites with TEPC 15 myeloma protein. Thus, anti-idiotypic antibodies directed against TEPC 15 myeloma protein function as "anti-receptor" antibodies since they specifically prevent induction of the primary response to phosphorylcholine. It is proposed that antibodies to receptors may be involved in the homeostasis of the immune response.