The Halogen assay is a new technique for measuring airborne allergen. The assay is unique in that it is capable of analyzing allergens and particles together, combining the advantages of morphological approaches and immunoassay. The Halogen assay allows direct observation of the particles that carry the allergen as well as being capable of identifying all the allergen sources an individual is exposed and sensitized to. The assay is sensitive because the extracted allergen is bound to the membrane at a high local concentration within the minute area around each particle and so is easily detected by immunostaining. It is therefore easy to detect few pollen grains. The Halogen method supersedes other methods commonly used to identify allergens as it is capable of identifying airborne particles that are allergen sources.