The aim of this study was to test the hypothesis that the mechanism of recruitment and the lower knee of the pressure-volume (P-V) curve in the normal lung are primarily determined by airway reopenings via avalanches, rather than simple alveolar recruitments. In isolated dog lung lobes, the P-V loops were measured and crackle sounds were recorded intrabronchially during both the first inflation from the collapsed state to total lobe capacity (TLC) and a second inflation without prior degassing. The inflation flow contained transients which were accompanied by a series of crackles. Discrete volume increments (V) were estimated from the flow transients and the energy (E) of the corresponding crackles were calculated from the sound recordings. Crackles were concentrated in the early phase of inflation with the cumulative energy exceeding 90% of its final value by the lower knee of the P-V curve. The values of V were correlated with E during the flow transient for both the first and the second inflations (r²=0.29-0.73 and 0.68-0.82, respectively). Since the distribution of V followed a power law, the correlation between crackle energy and discrete volume increments suggests that an avalanche-like airway opening process governs the recruitment of collapsed normal lungs.