Celiac disease (CD) is most probably an immunological disease, precipitated in susceptible individuals by ingestion of wheat gliadin and related proteins from other cereals. The disease shows a strong HLA association predominantly to the cis- or trans-encoded HLA-DQ(alpha1*0501, beta1*02) (i.e., DQ2) heterodimer. T cell recognition of gliadin peptides presented by DQ2 in the intestinal mucosa is central in the immunopathogenesis of CD. Here we describe a study where overlapping peptides from the N-terminal region of alpha-gliadin have been tested in biochemical assays for binding to affinity-purified DQ2 and DR3 (i.e., DR(alpha, beta1*0301)) molecules. The peptides were also tested for binding to DQ2 in a functional binding assay, where binding was measured as the capacity to inhibit the stimulation of a gliadin-specific, DQ2-restricted T lymphocyte clone RNnTalpha33. In both assay systems the overlapping gliadin peptides were found to bind with weak or intermediate affinity to DQ2. No or only very weak binding was found to DR3 in the biochemical binding assay. Overall, the results question the role of these peptides in the T-cell-mediated immunopathogenesis of CD. The in vitro assays described here provide new methods for the screening of potentially toxic peptides.