We examined the ultrastructures of the tongue squamous cell carcinomas which received radiotherapy and compared the metastatic cases with the non-metastatic cases. The results were as follows:
1. The non-metastatic cases were clinically T1N0 or T2N0 and histologically Grade I or II of the WHO classification. Electronmicroscopic observation of these cases revealed that numerous microvilli and a small number of desmosomes were found and the cell attachment seemed to be weak. These findings were different from those of the non-metastatic cases which received surgery.
2. In the metastatic cases of which the primary lesions were controlled, microvilli were not developed and a number of desmosomes were shown as compared with those in the nonmetastatic cases. However, cell atypia and dispersion of the nuclear chromatin were clearly recognized.