Thyroglobulin is produced only by thyroid follicular cells, and has a molecular weight of 660,000 and carbohydrate content of approximately 10%. The composition of carbohydrate chains on thyroglobulin from thyroid carcinoma has been reported to differ from that in normal thyroid tissue. In this study, heterogeneities of carbohydrate chains on thyroglobulin obtained from thyroid tissues were investigated by competitive reaction between lectin and anti-thyroglobulin monoclonal antibody. Concanavalin A, Lens culinaris agglutinin, Ricinus communis agglutinin-120 and Datura stramonium agglutinin were compared. The ratio of Lens culinaris agglutinin-reactive thyroglobulin to thyroglobulin was significantly lower in thyroid carcinoma than in normal thyroid tissue, Graves' disease and benign thyroid tumor. However, no differences between malignant and benign tissues were observed with the other lectins tested. Differences in carbohydrate chain on thyroglobulin were observed between malignant and benign thyroid tissues.