We examined the effect of intraesophageal acid (either spontaneous gastroesophageal reflux or infused) on airflow resistance in 15 sleeping asthmatic subjects. We observed no significant acute or sustained changes in airflow resistance relative to periods of intraesophageal acid. Overnight changes in spirometry and lower airway resistance also demonstrated similar nocturnal worsening of bronchoconstriction despite the occurrence of spontaneous or simulated gastroesophageal reflux. The presence or absence of clinical evidence of esophagitis (Bernstein test response) did not alter the observed lack of response to intraesophageal acid. We conclude that gastroesophageal reflux contributes little to the nocturnal worsening of asthma.