Changes of surface sugar residues in the large intestinal mucosa may be associated with malignant transformation and may be of importance in differentiating borderline lesions. To compare these changes in normal mucosa, adenomas, and carcinomas of the large intestine, we investigated modifications of carbohydrate composition, such as those of N-acetyl-galactosamine (GalNac), L-fucose, and o-acetylated sialic acid, by histochemical staining with Dolichos biflorus agglutinin (DBA) and Ulex europaeus agglutinin-1 (UEA-1) lectins, and with Culling's periodic acid-thionin Schiff/potassium hydroxide/periodic acid-Schiff (PAT/KOH/PAS), respectively. For stable staining, the sections stained with DBA and UEA-1 were pretreated with potassium hydroxide and neuraminidase. We conclude that the pattern of the two lectin stainings in carcinomas is quite different from that in normal mucosa and adenomas, and that it shows the carcinomatous features in some cases of adenoma with severe atypia (borderline lesions). In contrast, PAT/KOH/PAS staining demonstrates differences between normal mucosa and adenomas rather than differences between adenomas and carcinomas.