We have investigated the importance of cell-surface serine- and/or threonine-linked oligosaccharide adhesion molecules synthesized by the Golgi enzyme core 2 -1,6-N-acetylglucosaminyltransferase (C2GlcNAcT) in mediating eosinophil trafficking to the lung in studies utilizing C2GlcNAcT-I-deficient mice. The number of bronchoalveolar eosinophils, the number of lung eosinophils, and airway responsiveness to methacholine were not significantly different in C2GlcNAcT-I-deficient compared with wild-type mice sensitized and challenged by inhalation with ovalbumin. C2GlcNAcT-I-deficient mice do not demonstrate defects in neutrophil trafficking to the lung in response to lipopolysaccharide (LPS). In contrast, ragweed-sensitized C2GlcNAcT-I-deficient mice exhibit significantly reduced eosinophil trafficking to the peritoneal cavity in response to ragweed peritoneal challenge. C2GlcNAcT-I-deficient mice also have significantly reduced neutrophil trafficking to the peritoneal cavity in response to LPS challenge. Overall, these studies demonstrate an important role for serine/threonine-linked oligosaccharides synthesized by the Golgi enzyme C2GlcNAcT-I in eosinophil and neutrophil trafficking to the peritoneum but not for eosinophil or neutrophil trafficking to the lung.