Lectin methods have increased the capacity for histochemical characterization and differentiation of glycoproteins and have demonstrated, for example, greater reactivity of gastrointestinal than of respiratory tract secretions with the periodate-concanavalin A-horseradish peroxidase method for localizing mannose-rich glycoprotein. Application of a battery of ultrastructural cytochemical methods with specificity for the constituents characteristically present in the complex carbohydrates provides knowledge of the distribution of the various recognizable types of glycoconjugates in tissues and cells showing, for example, marked differences in glycoconjugates of the apical compared with the basolateral plasmalemma in a given cell type and differences between apical plasmalemmas or basement membranes of different cell types. Such information raises questions as to the biologic significance of the different complex carbohydrates in various sites and, hopefully, will lead to a clearer understanding of their physiologic roles.