I. Serial histopathologic study of esophageal squamous cell carcinoma. A review of 335 cases of squamous cell carcinoma disclosed 55 cases (16.4%) with glandular components in addition to the ordinary component of squamous cell carcinoma, suggesting that this type of esophageal tumor had originated not only from the covering squamous epithelium but from esophageal gland or ductal epithelium. Intra-epithelial carcinoma concomitant with squamous cell carcinoma was seen in 95 cases (28.4%). The incidences of coexistence in such lesion were higher in the groups of early stage esophageal cancer. These observations support the concept of field carcinogenesis of esophageal cancer. II. Histopathologic study of squamous epithelial dysplasia. Among 91 cases without preoperative treatment, there were 40 dysplastic lesions in 23 cases (25.3%). The continuity of dysplasia to the carcinoma was 48.3% and it was often encountered in severe dysplasia rather than in moderate or mild dysplasia, suggesting some relationship between the severity of dysplasia and carcinoma. III. Immunohistochemical study of EGF and c-myc. Among 27 cases, EGF was positive in 10 (37.0%). c-myc was positive in 18 (66.7%) not only cancer but normal epithelium suggesting that some change of products of oncogene occurred also in the normal epithelium of the patients of esophageal cancer.