The mucosal surface of the human lacrimal sac represents an area exposed to exogenous agents including potentially harmful microorganisms. The human lacrimal sac was examined histochemically to identify glycoproteins, and immunohistochemically to identify secretory IgA. Neutral and acid glycoconjugates were detected mainly in the cytoplasm of the surface cells of the columnar stratified epithelial lining. The same reactions were recognized in occasional clusters of secretory cells forming intraepithelial glands in the lining of the lacrimal sac, The presence of secretory IgA in the cytoplasm of the apical epithelial cells was demonstrated. The results indicate that the lacrimal sac mucosa possesses certain active defense mechanisms against ascending infections.