Ozone (O₃), a common air pollutant, induces airway inflammation and airway hyperresponsiveness. In mice, the neutrophil chemokines KC and macrophage inflammatory protein-2 (MIP-2) are expressed in the lungs following O₃ exposure. The purpose of this study was to determine whether CXCR2, the receptor for these chemokines, is essential to O₃-induced neutrophil recruitment, injury to lungs, and increases in respiratory system responsiveness to methacholine (MCh). O₃ exposure (1 ppm for 3 h) increased the number of neutrophils in the bronchoalveolar lavage fluid (BALF) of wild-type (BALB/c) and CXCR2-deficient mice. However, CXCR2-deficient mice had significantly fewer emigrated neutrophils than did wild-type mice. The numbers of neutrophils in the blood and concentrations of BALF KC and MIP-2 did not differ between genotypes. Together, these data suggest CXCR2 is essential for maximal chemokine-directed migration of neutrophils to the air spaces. In wild-type mice, O₃ exposure increased BALF epithelial cell numbers and total protein levels, two indirect measures of lung injury. In contrast, in CXCR2-deficient mice, the number of BALF epithelial cells was not increased by O₃ exposure. Responses to inhaled MCh were measured by whole body plethysmography using enhanced pause as the outcome indicator. O₃ exposure increased responses to inhaled MCh in both wild-type and CXCR2-deficient mice 3 h after O₃ exposure. However, at 24 h after exposure, responses to inhaled MCh were elevated in wild-type but not CXCR2-deficient mice. These results indicate CXCR2 is essential for maximal neutrophil recruitment, epithelial cell sloughing, and persistent increases in MCh responsiveness after an acute O₃ exposure.