The present study was undertaken to clarify the function of FcRγ⁺ and FcRγ^–– lymphocytes in anti-DNP IgE antibody responses. The helper activity was observed predominantly in FcRγ^–– T cells, but poorly in FcRγ⁺ T cells, as in the case of IgG antibody responses, indicating that the absence of FcRγ on T cell surface is a common surface characteristic to helper T cells, and that there is no close relationship between the determination of class specificity of Ig and T cell subsets divided by the presence or absence of FcRγ. Furthermore, IgE antibody responses were more dependent upon helper T cells than IgG antibody responses. The data presented in this paper also demonstrated that the precursors of anti-DNP IgE antibody-forming cells were equally contained in both FcRγ⁺ and FcRγ^–– B cells, when they were transferred into recipients with helper T cells. This is a striking contrast to IgM/IgG antibody responses, in which only FcRγ^–– B cells could differentiate into antibody-forming cells. Moreover, the precursor activity of FcRγ⁺ and FcRγ^–– B cells for IgE antibody-forming cells was not affected by the treatment of cells with suppressive B cell factor released from FcRγ⁺ B cells after binding of antigen-antibody (IgG) complexes and known to suppress the proliferation of FcRγ^–– IgM/IgG antibody-forming cell precursors. Thus, IgE B cells seem to be more heterogeneous than IgM/IgG B cells with respect to the FcRγ marker and insensitive to the regulatory effect of FcRγ⁺ B cells. IgE B cells are regulated differently from IgG B cells in B-B cell interactions.