Airway diameter and airway wall mechanics (compliance) are important determinants of flow limitation and wheezing. We have previously used the high-speed interrupter technique (HIT) to measure input impedance (Zin) in infants at frequencies up to 900 Hz, including antiresonance phenomena, which are known to be related to wave propagation velocity, and have shown that the frequency at which the first antiresonance occurs (f(ar,1)) is a function of airway wall compliance. We aimed to determine whether f(ar,1) (and thus airway wall compliance) was different in infants with a history of wheezing disorders. We compared 23 asymptomatic infants (aged 36 to 81 wk) with a history of wheezing with an age-matched group of 19 healthy control infants. We found that f(ar,1) was significantly lower in infants with wheezing disorders than in the control group (p < 0. 005), implying differences in airway wall compliance, even when they were clinically asymptomatic. Developmental differences in airway wall mechanics may be important in the pathogenesis of wheezing disorders or, alternatively, alterations in airway wall mechanics might be a consequence of postinflammatory remodeling.