97 cases of thyroid carcinoma originated from follicular epithelium were investigated by using histological and immunohistochemical techniques with special reference to lectin distribution. According to the WHO histological typing of thyroid tumours, these cases were divided into three categories as follows: papillary carcinoma of thyroid (PCT) 56, follicular carcinoma of thyroid (FCT) 31 and undifferentiated carcinoma of thyroid (UCT) 10. Results showed that three different kinds of thyroid carcinoma presented various hormone function and distribution of lectins. The positive rate of Tg immunoreactivity was significantly different between these three kinds of tumour, i.e. PCT greater than FCT greater than UCT. Additionally, the positive rate of T4 and T3 immunoreactivity was lower than that of Tg. Some Gastrin, SS and calcitonin positive cells were also recognized in carcinoma of thyroid. Lectin--binding rate of WGA, PNA, SBA and UEA to 97 cases of thyroid carcinoma and 9 cases of normal thyroid tissue revealed that different lectin had a selective binding activity to various types of thyroid carcinoma and normal thyroid cells. From the data obtained, it seemed that the morphological differentiation of thyroid carcinoma was in correspondence with difference of function, and the extent of cell differentiation may be closely related to the biological behavior of the tumour.