Under normal conditions, airborne allergens are present at very low concentrations. Allergens may be carried on relatively large identifiable particles such as grains of pollen and mould spores or smaller amorphous particles or both. The methods that have been applied to quantify animal airborne allergens will be described in this chapter. By careful selection of the air sampling equipment and conditions, samples can be collected which quantify, for example, the personal exposure of an individual when performing a specific task or changes in exposure when allergen control methods are implemented. If as with animal allergens, an airborne allergen is not comprised of identifiable microscopic fragments, it is necessary to extract the soluble allergen for quantification in a specific immunoassay. The basic methods used for the elution of animal allergen from polytetrafluoroethylene (PTFE) filters will be described. The optimization of this method to suit different allergens and the influence of the buffer on extraction efficiency and stability of the allergen during storage will also be discussed.