Immediate, type 1 allergic reactions occur following interaction between allergen, immunoglobulin E (IgE), and the mast cell or basophil. Allergen‐induced activation of these cells leads to the release of a number of mediators that are responsible for the symptoms observed during an allergic reaction. Recent progress in elucidating the structures, and in developing syntheses for platelet aggregating factor and the leukotrienes, promises to increase our understanding of the immunopharmacology of allergic and inflammatory reactions. The need for the standardization of allergen extracts is emphasized, and current activity in this area is highlighted.