Technical Abstract: In the majority of patients, roasted peanuts resulted in a higher skin prick test (SPT). Purified Ara h 1, Ara h 2, and Ara h 3 from roasted peanut binds higher IgE levels than from raw peanuts. To determine if there are any structural changes; and if these changes contribute to increased IgE binding by the proteins purified from roasted peanuts, we assessed the secondary structure of each allergen purified from raw, light roast, and dark roast peanut, and compared the differences in IgE binding to these allergens. Ara h 1, 2, and 3 were purified from raw (R), light roast (LR), and dark roast (DR) peanuts. The IgE binding to each of these proteins was compared using sera from peanut allergic and sensitized, but tolerant patients, using immunoblot analysis. Circular dichroism (CD) was used to monitor the structural changes. While the structure of the allergens did not show large changes when purified following various roasting processes, the IgE binding to the roasted samples increased significantly with time of roasting. The chemical modifications incurred by roasting are more important for IgE binding than processing induced structural changes. Understanding the differences in IgE binding to various processed forms of foods by allergic versus sensitized patient sera may be useful in development of more specific diagnostic tools, and potentially processes that can result in reduced allergenicity of a food.