Myasthenia gravis (MG) is a T cell-dependent, Ab-mediated autoimmune disease. T cells reactive to a dominant peptide alpha 146-162 of acetylcholine receptor (AChR) alpha subunit participate in murine MG pathogenesis. To suppress the autoimmune response to AChR, a high dose of alpha146-162 peptide in IFA was administered parenterally as a tolerogen, after the development of a primary T cell immune response to AChR. This form of AChR T cell peptide tolerance suppressed the in vitro T cell proliferative response to AChR and its dominant alpha146-162 and subdominant alpha182-198 peptides through epitope spread. Administration of alpha146-162 peptide in IFA after the primary immune response to AChR also significantly suppressed the serum anti-AChR Ab of the IgG2b isotype and clinical incidence of MG in C57BL/6 mice. Furthermore, the production of IFN-gamma, IL-2, and IL-10 cytokines by AChR, alpha146-162, and alpha182-198 peptide-reactive cells was suppressed by alpha146-162 peptide tolerance, and the epitope spread observed could be attributed to the reduction in the above cytokine production. Therefore, AChR T cell-dominant peptide tolerance could be adapted in the Ag-specific therapy of MG.