Reactive airway disease may be related to genetic, infectious, and environmental factors. The latter two have been well documented, but there are no data on nonspecific airway responsiveness in normal infants prior to any insult to the respiratory tract. We measured forced expiratory flow by the thoracic compression technique and lung volume in 30 normal infants before and after challenge with cold, dry air (CDA) and compared the results with those in 12 infants who did not receive CDA challenge. As a group, infants challenged with CDA had a mean decrease in VmaxFRC of 17.9 +/- 24.1% SD. This was significantly different (P less than 0.01) from the lack of change (+ 1.3 +/- 18.1% SD) seen in the control group. We conclude that nonspecific airway reactivity may exist from early infancy and may predate any known lung injury. The relationship of this airway responsiveness to subsequent reactive airway disease and other respiratory illnesses is unknown and requires longitudinal study.