The effect of prolonged exposure to either positive or negative small air ions was studied in nine patients with bronchial asthma, of whom seven had reported increased respiratory symptoms in association with weather changes. On consecutive days, while grounded, patients were exposed for six hours to approximately 10,000/cc of either positive or negative ions. Pulmonary function, pulse and blood pressure were measured throughout the exposure. Questionnaires to assess emotional state and physical symptoms were completed after 15 minutes and five hours each day. Urinary 5-hydroxy indoleacetic acid (5HIAA) excretion was measured. Patients were continued on theophylline but adrenergics and corticosteroids were withheld. No patient experienced an exacerbation of asthma. Symptoms, pulmonary function, pulse and blood pressure, urinary 5HIAA excretion and the response to the questionnaires did not differ significantly between the two ion exposures. Thus moderately long exposure to positive or negative small air ions did not influence the clinical condition of these patients, many of whom reported exacerbations with weather changes. The findings do not support a significant role of small air ions in exacerbations or treatment of bronchial asthma.