Allergy is routinely taken into account in asthma. The allergic reaction is based on Th2 lymphocytes specific to the allergen, which induce production of E immunoglobulins (IgE) and activation of eosinophils. In atopic asthma, domestic allergens are more often responsible than pollen. They play a part early in the development of the disorder, and subsequently as factors triggering exacerbations. Work-related asthma should always be suspected. History-taking should seek the relevance of allergens in the clinical manifestations, confirmed by skin tests, and if necessary assessment of specific IgE. Provocation tests should be used only diagnosis of work-related asthma. Removal of allergens should be suggested. Specific desensitisation may be indicated in order to decrease high-dosage drug treatment. Rhinologic treatment is part of patient management. Treatments being developed include the use of anti-IgE antibodies, anti-interleukin (IL)-5, soluble IL-4 receptors and recombinant allergens.