Previous studies have shown that Hsp72 is found in the extracellular space (eHsp72) and that eHsp72 has potent immunomodulatory effects. However, whether eHsp72 is present in the distal airspaces and whether eHsp72 could modulate the removal of alveolar edema is unknown. The first objective was to determine whether Hsp72 is released within the airspaces and whether Hsp72 levels in pulmonary edema fluid would correlate with the capacity of the alveolar epithelium to remove alveolar edema fluid in patients with ALI/ARDS. Patients with hydrostatic edema served as controls. The second objective was to determine if activation of the stress protein response (SPR) caused the release of Hsp72 into the extracellular space in vivo and in vitro and to determine whether SPR activation and/or eHsp72 itself would prevent the IL-1 mediated inhibition of the vectorial fluid transport across alveolar type II cells. We found that eHsp72 was present in plasma and pulmonary edema fluid of ALI patients and that eHsp72 was significantly higher in pulmonary edema fluid from patients with preserved alveolar epithelial fluid clearance. Furthermore, SPR activation in vivo in mice and in vitro in lung endothelial, epithelial and macrophage cells caused intracellular expression and extracellular release of Hsp72. Finally, SPR activation, but not eHsp72 itself, prevented the decrease in the alveolar epithelial ion transport induced by exposure to IL-1. Thus, SPR may protect the alveolar epithelium against oxidative stress associated with experimental ALI, and eHsp72 may serve as marker of SPR activation in the distal airspaces of patients with ALI.