To demonstrate the existence and assess the magnitude of reflex bronchoconstriction in asthmatics, triggered by gastroesophageal reflux, pulmonary function studies (forced expiratory spirogram, flow-volume loops and airway resistance) were performed during a Bernstein test in 21 adult patients with intrinsic asthma and in 15 controls. Six asthmatics and 7 controls had symptomatic reflux test and a positive standard acid reflux test. Bernstein test was positive in all symptomatic individuals and in 2 asthmatics with a negative standard acid reflux test. Changes in pulmonary function occur only in asthmatics with symptomatic reflux. Decreases were: FEV1 8.4 +/- 3.4; FEF25-75% 45 +/- 7.3; Vmax 15 +/- 8.4; and Sgaw 16 +/- 3.7. Although changes were statistically significant (p less than 0.05), the magnitude of decrease is rather small and unlikely to be felt by an asthmatic or produce wheezy dyspnea. Therefore, even though the presence of acid in the lower esophagus may produce reflex bronchoconstriction in some asthmatics with symptomatic reflux, this appears to be of little significance.