Abstract 1. 1. Airway resistance has been measured by means of a body plethysmograph and in normal subjects found to be 1.25 ± .22 cm. H 2O per L. per sec. 2. 2. Airway resistance in patients with bronchial asthma ranged between 2.0 and 9.6 cm. H 2O per L. per sec. 3. 3. Resistance values above the normal range were found in patients with bronchial asthma who had neither signs nor symptoms of their disease at the time tested. 4. 4. Airway resistance in asymptomatic patients ranged between 2.0 and 5.5 cm. H 2O per L. per sec. Resistance in symptomatic patients ranged between 4.3 and 9.6 cm. H 2O per L. per sec. 5. 5. Nebulized isoproterenol produced a significant reduction of airway resistance in both groups. 6. 6. Poor correlation was found between airway resistance and first-second vital capacity.