In order to understand the migration mechanism and character of eosinophils in the nose, the eosinophils in nasal mucosa and secretion were observed morphologically and physicochemically. In our electron microscopic observation of animal and human nasal mucosa, eosinophils migrated through the intercellular space, projecting pseudopods into the apical region of the space and splitting the junctions between epithelial cells. However, a freeze-fracture study in the experimental animals showed that the morphology of tight junction was not significantly changed except for slight decrease in the number of strands in antigen challenged animals. Eosinophilotactic activity was clearly demonstrated in nasal secretion of patients with allergic rhinitis. The factor in nasal secretion was a molecule smaller than 10,000 and sensitive to heating in higher degree. Additionally, the eosinophils in nasal secretion were hypodense, implying that they may be in activated state.