BALB/c mice were immunized with purified phosphorylcholine (PC)-specific myeloma protein of the TEPC-15 tumor, which bears the major idiotype of the anti-PC response (T15 Id) in this mouse strain. Four months after establishing the anti-idiotypic response, animals were immunized with PC-keyhole limpet hemocyanin under conditions which normally lead to IgE antibody formation. The expression of anti-PC antibodies of each immunoglobulin class was compared to a group of matched control mice not immunized with T15. In BALB/c mice producing anti-idiotypic antibodies the formation of anti-PC IgM, IgG1, IgG2, IgG3 and IgE was suppressed to various extents and for different lengths of time. An exception to this observation was the formation of anti-PC IgA antibodies, in that no significant difference was measured between the two groups of mice. BALB/c mice immunized in the same way with the PC-specific myeloma proteins of the MOPC-167, MOPC-511 and MOPC-603 tumors produced normal levels of anti-PC IgE and IgG antibodies. These results suggest that T15 idiotype-positive antibodies are probably formed within all classes of specific antibodies expressed during an immune response to PC. The possibility of extending the phenomena of anti-idiotype-induced suppression to the level of various classes of specific antibodies, including IgE, might be of interest in the treatment of some allergic diseases.