It is well recognized that CD8 T cells inhibit IgE responses. In this study, we investigated the mechanism of CD8 T cell-mediated IgE suppression by comparing the capacity of T cytotoxic 1 (Tc1) and T cytotoxic 2 (Tc2) CD8 T cells to inhibit IgE responses to ovalbumin (OVA). Tc1 and Tc2 CD8 T cells were generated from OVA 257–264-specific Vβ5. 2 T cell receptor (TcR) transgenic mice by stimulation with anti-CD3 and anti-CD28 under Tc1 and Tc2 polarizing conditions. Tc1 and Tc2 Vβ5. 2 TcR CD8 T cells (10 6) were adoptively transferred to syngeneic mice, and following immunization with 100 µg of OVA/alum, serum IgE antibodies were measured by passive cutaneous anaphylaxis and expressed as the highest dilution that gave a detectable skin response. Both Tc1 and Tc2 CD8 T cells from OT-I mice inhibited IgE. Both Tc1 and Tc2 CD8 T cells promote Th1 immunity and inhibit IgE responses. This process appears to be independent of CD8 T cell-derived IFN-γ, as both Tc2 (IFN-γ–) and Tc1 (IFN-γ+) CD8 T cells inhibited IgE.