Embryonic muscle acetylcholine receptor (AChR) is composed of four subunits—α,β,γ andδ. Upon innervation, the γ subunit is substituted by a homologous ϵ subunit. Embryonic muscle AChR might be the original autoantigen in Myasthenia gravis (MG) because it is expressed in the thymus, where the anti-AChR response might start, as well as in adult extrinsic ocular muscles, which are a preferential target in MG. MG patients have antibodies specific for embryonic AChR and CD4⁺T cells, which recognize epitopes on the γ subunit, in association with DR molecules. In the present study, we investigated the binding to several purified DR molecules (DRB10101, DRB10201, DRB10401 and DRB10701) of overlapping synthetic peptides, screening the human γ subunit sequence. Binding of the peptides to the DR molecules was determined from their ability to compete with radiolabelled peptide probes for binding to purified DR molecules. All peptides which were recognized by CD4⁺cells bound to the relevant DR molecule. On the other hand, some AChR peptides not recognized by CD4⁺cells of MG patients bound well to one or more DR molecules. In terms of relative ability to bind to the DR molecules tested, the γ subunit behaved like an exogenous antigen: some AChR peptide sequences uniquely bound one DR molecule, others bound several DR alleles, while others did not bind any of the DR molecules tested.