The autoreactive response in murine experimental autoimmune encephalomyelitis (EAE) is dominated by an oligoclonal expansion of Vβ8+ CD4+ T cells. These T cells recognize the immunodominant N-terminal nonapeptide of myelin basic protein (MBP1–9) associated with the MHC class II molecule, I-Au. Amongst the autoreactive cells, T cells bearing TCR containing the CDR3β motif Asp-Ala-Gly-Gly-Gly-Tyr (DAGGGY) play a dominant role in the disease process. Here we have investigated the molecular basis for antigen recognition by a representative TCR (172.10) that contains the DAGGGY motif. The roles of the three glycines in this motif in the corresponding TCR-peptide-MHC interactions have been analyzed using a combination of site-directed mutagenesis and surface plasmon resonance. Our data show that mutation of either of the first two glycines (G97, G98) to alanine results in soluble, recombinant TCR that do not bind to recombinant antigen at detectable levels. Mutation of the third glycine (G99) of the 172.10 TCR results in a substantial decrease in affinity. The importance of the triple glycines for antigen recognition provides an explanation at the molecular level for the recruitment of T cells bearing the DAGGGY motif into the responding repertoire during EAE induction.