Lectins conjugated to horseradish peroxidase were used to stain paraffin sections of mouse, rat, and human respiratory tract tissues. An additional method was applied utilizing galactose oxidase to oxidize the C-6 hydroxyl of galactose and N-acetylgalactosamine residues and the resulting aldehyde was visualized with 2% Schiff's reagent. Sections were stained prior to and after removal of sialic acid residues. Oligosaccharides with terminal beta-galactose and alpha-N-acetylgalactosamine residues were found in all serous cells in the mouse trachea but were never seen in human tracheal serous cells. About 5-10% of serous cells in the rat trachea contained terminal beta-galactose, whereas all human tracheal serous cells and the remainder of those in the rat contained oligosaccharides with terminal sialic acid and penultimate beta-galactose residues. Fucose was not detected in tracheal serous cells of any species. Mucous cells in the mouse and rat trachea produced heterogeneous oligosaccharides containing terminal alpha-N-acetylgalactosamine and/or terminal sialic acid residues in various proportions. The structure of oligosaccharides in human tracheal mucous cells varied between individuals and was related to ABO blood group reactivity. The majority of oligosaccharides in type A individuals contained terminal alpha-N-acetylgalactosamine, whereas type AB individuals had approximately equal amounts of terminal alpha-galactose and alpha-N-acetylgalactosamine residues. Mucous cells in the two type O specimens examined contained a large amount of terminal beta-galactose and surprisingly, terminal fucose was not detected in these individuals. These results support biochemical studies showing structural diversity in oligosaccharide chains of respiratory tract secretions and reveal differences in glycoprotein secretion of different cell types.