Preferential eosinophil accumulation is characteristic of airway inflammation in asthma. Although little is known about its mechanism, the effect of a sialyl Lewis X analog on airway eosinophilia was examined in a guinea-pig model of asthma. Guinea-pigs were sensitized by repeated inhalation of ovalbumin. After a single inhalation challenge, the animals showed striking airway eosinophilia and a late asthmatic response. In contrast, when guinea-pigs were pretreated intravenously with sialyl Lewis X analog (LX 0104) 1 h before antigen challenge, both eosinophil infiltration in the tracheal wall and the late asthmatic response were significantly inhibited in a dose-dependent manner. In a further in vitro study, LX 0104 significantly suppressed the adhesion of human and guinea-pig eosinophils to human umbilical vein endothelial cells activated with interleukin-1 beta. These results suggest that LX 0104 plays a critical role in antigen-induced airway eosinophilia and the late asthmatic response.