Hepatic ischemia/reperfusion results in an acute inflammatory response culminating in the recruitment of activated neutrophils which directly injure hepatocytes. Recent evidence suggests that CD4⁺ lymphocytes may regulate this neutrophil-dependent injury, but the mechanisms by which this occurs remain to be elucidated. In the present study, we sought to determine the type of CD4⁺ lymphocytes recruited to the liver after ischemia/reperfusion and the manner in which these cells regulated neutrophil recruitment and tissue injury. Wild-type and CD4-knockout (CD4^-/-) mice were subjected to hepatic ischemia/reperfusion. CD4⁺ lymphocytes were recruited into the liver within 1 hour of reperfusion and remained for at least 4 hours. These cells were comprised of conventional (TCR-expressing), unconventional (TCR-expressing), and natural killer T cells. CD4^-/- mice were then used to determine the functional role of CD4⁺ lymphocytes in hepatic ischemia/reperfusion injury. Compared to wild-type mice, CD4^-/- mice had significantly greater liver injury, yet far less neutrophil accumulation. Adoptive transfer of CD4⁺ lymphocytes into CD4^-/- mice recapitulated the wild-type response. In wild-type mice, neutralization of IL-17, a cytokine released by activated CD4⁺ lymphocytes, significantly reduced neutrophil recruitment in association with suppression of MIP-2 expression. Finally, oxidative burst activity of liver-recruited neutrophils was higher in CD4^-/- mice compared to those from wild-type mice. These data suggest that CD4⁺ lymphocytes are rapidly recruited to the liver after ischemia/reperfusion and facilitate subsequent neutrophil recruitment via an IL-17-dependent mechanism. However, these cells also appear to attenuate neutrophil activation. Thus, the data suggest that CD4⁺ lymphocytes have dual, opposing roles in the hepatic inflammatory response to ischemia/reperfusion.