Normal control subjects will be individuals who are in good overall health, age and sex matched to the asthmatic group, age 18 - 50 and nonallergic, i.e. entirely negative on the panel of prick skin tests with no history of allergic rhinitis or asthma, no history of allergic symptoms caused by cats or dust mite allergen exposure, life-long nonsmokers of cigarettes (defined as a lifetime total of less than 5 pack-years and none in 5 years), normal spirometry (i.e. FEV1 and FVC of at least 90% of predicted) and with a methacholine PC20 of > 16 mg/ml.