Using the AllerScan phage display library, we identify thousands of IgE and IgG antibody reactivities against hundreds of distinct organisms with peptide level resolution. We identify robust differences in the anti-wheat IgE reactivities of wheat allergic individuals compared to both non-allergic and wheat-sensitized individuals. Finally, we identify a wheat allergen epitope in alpha purothionin that may prove to be particularly useful in distinguishing wheat allergy from wheat sensitization. AllerScan is a massively multiplexed serological assay with utility for correlating clinical characteristics with anti-allergen IgE and IgG reactivity at cohort scale.