ABSTRACT: High-mobility group box (HMGB) 1 is a recently discovered proinflammatory mediator that contributes to acute lung injury. We determined HMGB-1 levels in bronchoalveolar lavage fluid of patients during mechanical ventilation (MV) and ventilator-associated pneumonia (VAP). Bronchoalveolar lavage fluid was obtained from patients who were ventilated for 5 h because of an elective surgical procedure ("short-term MV"; n = 40) or for several days because of respiratory failure without acute lung injury ("long-term MV"; n = 10) and from patients who developed unilateral VAP (n = 4). Ten healthy volunteers served as controls. In healthy volunteers, HMGB-1 levels were low (median, 1.6 ng mL−1; interquartile range [IQR], 0.7 - 3.7 ng mL−1). Although HMGB-1 levels were elevated after short-term MV, differences were not statistically significant compared with healthy volunteers (1.7 ng mL−1; IQR, 0.8 - 8.5 ng mL−1, P = 0.493 vs. healthy volunteers; P = 0.250 vs. start of MV). However, HMGB-1 levels were significantly higher in "long-term" MV patients (11.7 ng mL−1; IQR, 8.7 - 37.0 ng mL−1; P < 0.0001 vs. healthy volunteers). With unilateral VAP, HMGB-1 levels from the infected lung were 17.4 (IQR, 8.5 - 23.2) ng mL−1 (P = 0.014 vs. healthy controls); these levels were not different from those measured in the contralateral noninfected lung (P = 0.625). Summarized, long-term MV is associated with increased HMGB-1 levels in contrast to "short-term" MV. In addition, HMGB-1 levels during VAP are increased compared with healthy volunteers; however, they are not different from those found in patients intubated and mechanically ventilated for a similar period of time.