Increasing evidence from case control surveys, population studies and allergen avoidance studies suggest inhalant allergy plays an important role in the etiology of asthma. Recent studies in hospital emergency rooms have compared the prevalence of serum IgE antibodies to common allergens (mite, cat, cockroach, rye grass and ragweed pollen) in patients admitted with acute asthma attacks and in unselected age-matched control subjects. These studies, carried out in central Virginia and northern California, showed a highly increased prevalence of IgE antibodies to inhaled allergens among asthmatic patients, and suggest that the development of allergen specific IgE antibody responses is a major risk factor for emergency room admission with asthma. Presentation at the emergency room appeared to be related to patients' exposure to specific allergens: in central Virginia, in the fall, dust mite was the predominant allergy, whereas in northern California, in May-June, most asthmatic patients (greater than 90 percent) were allergic to rye grass. New immunoassay technology, based on the use of monoclonl antibodies, has been developed to measure the quantities of "indoor" allergens (mite, cat, cockroach) in asthmatic patients' houses. It is now possible to propose tentative levels of mite allergens which should be considered both as a risk for IgE antibody sensitization (2micrograms allergen/g dust) and as a risk for acute asthma attacks (10micrograms allergen/g dust). Future management of asthma will require analysis of indoor allergens and the development of efficient allergen avoidance procedures. Further research is necessary to investigate the relationship between airborne allergen levels, particle size and the precipitation of asthma attacks and also to investigate immunologic mechanisms which may cause bronchial hyperreactivity.