This study investigates the role of high-mobility group box 1 (HMGB1) in hepatic ischemia-reperfusion (I/R) injury. HMGB1, a nuclear protein, is typically released as a late mediator of systemic inflammation in sepsis but acts as an early mediator of inflammation and organ damage in I/R injury. The authors found that HMGB1 levels increased early after reperfusion in the liver, up to 24 hours, and that inhibiting HMGB1 activity with neutralizing antibodies significantly reduced liver damage. Conversely, administering recombinant HMGB1 worsened I/R injury. Treatment with neutralizing antibodies was associated with reduced phosphorylation of c-Jun NH2-terminal kinase and increased nuclear factor-κB DNA binding in the liver. Additionally, Toll-like receptor 4 (TLR4)-deficient mice exhibited less damage compared to wild-type mice, and anti-HMGB1 antibodies provided protection in wild-type but not TLR4-deficient mice. These findings suggest that HMGB1 is an early mediator of injury and inflammation in liver I/R and that TLR4 plays a crucial role in this process.This study investigates the role of high-mobility group box 1 (HMGB1) in hepatic ischemia-reperfusion (I/R) injury. HMGB1, a nuclear protein, is typically released as a late mediator of systemic inflammation in sepsis but acts as an early mediator of inflammation and organ damage in I/R injury. The authors found that HMGB1 levels increased early after reperfusion in the liver, up to 24 hours, and that inhibiting HMGB1 activity with neutralizing antibodies significantly reduced liver damage. Conversely, administering recombinant HMGB1 worsened I/R injury. Treatment with neutralizing antibodies was associated with reduced phosphorylation of c-Jun NH2-terminal kinase and increased nuclear factor-κB DNA binding in the liver. Additionally, Toll-like receptor 4 (TLR4)-deficient mice exhibited less damage compared to wild-type mice, and anti-HMGB1 antibodies provided protection in wild-type but not TLR4-deficient mice. These findings suggest that HMGB1 is an early mediator of injury and inflammation in liver I/R and that TLR4 plays a crucial role in this process.