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 listed in section V (Study Procedures), 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.