The value (in terms of decreased numbers of attacks and of hospitalizations for attacks, decreased need for asthma medications, and improved tolerance to allergens) of rush immunotherapy to a mixture of allergens was studied in children with multiple sensitizations and severe asthma (as evaluated on the number of attacks, number of hospitalizations, and dependence on corticosteroids) already receiving optimal medical therapy. Because syndromic reactions are common, rush immunotherapy should be performed in the hospital and premedication with corticosteroids may be warranted in the most severe cases.