Preferential eosinophil accumulation is a characteristic of airway inflammation in asthma. Although little is known about its mechanism, recent in vitro observations suggest that the very late activation antigen-4 (VLA-4, CD49d/CD29) and vascular cell adhesion molecule-1 (VCAM-1) adhesion pathway may be involved in specific eosinophil migration. To test this hypothesis, we studied the effect of an anti-VLA-4 monoclonal antibody (mAb) on the airway eosinophilia in a guinea pig model of asthma. Guinea pigs were sensitized by repeated inhalation of ovalbumin. After a single inhalation challenge, the animals showed a striking airway eosinophilia and late asthmatic response (LAR). In contrast, when guinea pigs were pretreated intravenously at 2 h before antigen challenge with a rat antimouse VLA-4 mAb, PS2/3, cross-reacting with guinea pig eosinophils and lymphocytes, eosinophil, basophil and lymphocyte infiltration in the tracheal wall was significantly inhibited as well as LAR in a dose-dependent manner. These results suggest that VLA-4 plays a critical role in antigen-induced airway eosinophilia and LAR.