We examined the changes in maximum expiratory flow (.ovrhdot.Vmax) and the density dependence of maximum expiratory flow (.DELTA..ovrhdot.Vmax) during histamine-induced bronchoconstriction in dogs. Histamine acid phosphate solution was nebulized into the airways of six dogs to produce predominantly peripheral airway obstruction. .ovrhdot.Vmax air, .ovrhdot.Vmax with the dogs breathing 80% He-20% O2 (.DELTA..ovrhdot.Vmax), and airway sites of flow limitation (choke points) were examined at four lung volumes (VL), which ranged from 51 to 23% of the control vital capacity (VC). The findings were interpreted in terms of the wave-speed theory of flow limitation. At all VL, .ovrhdot.Vmax air decreased during bronchoconstriction by .apprx. 30% compared with the control value. Resistances peripheral to a 0.3-cm-diam airway were increased about threefold with histamine, whereas resistances between 0.6-cm-diam bronchi and main-stem bronchi increased just slightly. Airway diameters were measured in the air-dried lung at 20 cmH2O transpulmonary pressure. Our results showed that only at 44% VC did .DELTA..ovrhdot.Vmax decrease in all experiments after histamine to indicate peripheral obstruction (mean: 68.5 to 45%). At 23% VC, .DELTA..ovrhdot.Vmax increased slightly, from 22 to 28%. At 23 and 36% VC, substantial differences in the wave-speed variables between air and HeO2 were present before bronchoconstriction, so that .DELTA..ovrhdot.Vmax was low in some dogs, although peripheral airway obstruction was not evident. When bronchoconstriction was produced, .DELTA..ovrhdot.Vmax at 23% VC could not be decreased further and even increased in four of six dogs. Thus changes in .DELTA..ovrhdot.Vmax at given lung volume may not reflect the predominant site of airflow obstruction during bronchoconstriction.