Heterogeneity is a fundamental property of airway constriction; however, whether it is a distinguishing feature of mild asthma is not clear. We used computerized tomography and the forced oscillation technique to compare lung heterogeneity between 18 mild asthmatic and 19 healthy control subjects at similar levels of bronchoconstriction while supine. We also assessed the effects of deep inhalation and albuterol on supine lung mechanics. Measures of heterogeneity included lung attenuation, from which we derived a novel index of airspace size, and the frequency dependence of respiratory system resistance between 1-20 Hz. We found that asthmatic subjects had airways hyperresponsiveness to methacholine in the sitting position compared to controls, but both groups had similar falls in FEV₁ after inhaling methacholine while supine. There were no baseline differences between the groups in the frequency dependence of resistance, or lung attenuation, before methacholine, and both groups responded similarly with an increase in airspace size (+9.2% vs. +3.4%), airspace size heterogeneity (+9.8% vs. +4.2%), and frequency dependence of resistance (+76% vs. +86%) after methacholine. Deep inhalation did not affect resistance in either group, but albuterol significantly reduced resistance in both groups. We conclude that both computerized tomography and the forced oscillation technique demonstrate increased heterogeneity of airway narrowing during induced bronchoconstriction while supine, and that this heterogeneity is equivalent between subjects with mild asthma and healthy controls when bronchoconstricted to the same degree. Thus, heterogeneity appears to be a fundamental feature of bronchoconstriction, and is not unique to mild asthma.