MUC1 (DF3 antigen) is a member of a family of high molecular weight glycoproteins. Recent studies have demonstrated that MUC1 is expressed in tumors of various human organs and may function as an anti-adhesion molecule that inhibits cell-to-cell adhesion, inducing tumor metastasis. However, expression patterns of MUC1 have not yet been established in human esophageal carcinomas. In this study, we examined MUC1 expression and its histopathological localization in human esophageal squamous cell carcinoma. MUC1 immunoreactivity was found in 17 (32.1%) out of 53 esophageal squamous cell carcinomas, regardless of the depth of tumor invasion, vascular invasion or lymph node status. MUC1 expression was detected in the intramucosal part in 28.3% (15 out of 53) and in the invasive part in 32.6% (14 out of 43) of the esophageal carcinomas (no significant difference). These observations suggested that expression of MUC1 is an early event in cancer progression, but that it is not significantly associated with metastasis of human esophageal carcinomas.