The cellular distribution of the carbohydrates labeled by Dolichos bifluorus agglutinin (DBA), peanut agglutinin (PNA), and wheat germ agglutinin (WGA) were studied in 21 normal colonic mucosae, 17 transitional mucosae, 9 nonneoplastic polyps (NNP), 27 adenomas, and 25 colorectal carcinomas. In normal mucosa DBA bound selectively to mucin of the goblet cells in the upper colonic crypt and to apical cytoplasm of the superficial columnar cells with a strong linear pattern. PNA binding was present only in the supranuclear portion (Golgi area) of the cells. WGA showed a strong reactivity in the goblet-cell mucin and in the supranuclear portion and apical cytoplasm of columnar cells. Transitional mucosa (TM) showed a decrease in DBA binding to goblet-cell mucin, which was replaced by an increase in PNA reactivity. The DBA linear pattern in the apical cytoplasm of columnar cells was unmodified, however. Changes similar to those of TM were observed in juvenile and Peutz-Jeghers polyps. Adenomas showed a progressive loss of DBA reactivity and an increase in PNA positivity related to the degree of dysplasia. This change was more evident in the linear pattern of apical cytoplasm. Only 32% of the carcinomas reacted with DBA and those were mucinous and well-differentiated adenocarcinomas. WGA was positive in all carcinomas with a different pattern than in normal mucosa. These findings suggest that the different lectin-binding patterns in normal and neoplastic colonic mucosa are related to the degree of cellular differentiation. In the process of malignant transformation the carbohydrate distribution undergoes progressive changes through the adenoma-carcinoma sequence. These changes are related to the degree of dysplasia in adenomas and to the degree of differentiation in carcinomas.