A dual staining method has been developed to identify two types of mucous secreting cells in the gastric mucosa of human and rat in one and the same tissue section. Sections were stained first using the galactose oxidase-cold thionin Schiff (GOCTS) procedure and then with paradoxical Concanavalin A staining (PCS). Surface mucous cell mucin stained blue with GOCTS, whereas gland mucous cell mucin stained brown with PCS. This method enabled us to differentiate these two types of mucins not only in gastric epithelial cell cytoplasm but also in the extracellular space. Sugar residues detected by GOCTS were explored by employing four species of lectins, which were peanut and Allomyrina dichotoma agglutinins for beta-galactose and Vicia villosa and Wistaria floribunda agglutinins for beta-N-acetylgalactosamine. The effect of oxidation with galactose oxidase was also examined on the affinities of reactive sites for these lectins. The results indicated that, in the human stomach, the sugar residues responsible for this reactivity were most likely beta-N-acetylgalactosamine and beta-galactose in specimens lacking secretion of blood group determinants and beta-N-acetylgalactosamine in those showing the secretion. In the rat stomach, on the other hand, sugar residues responsible for GOCTS were not elucidated by these lectins.