It is sometimes difficult to identify scirrhous carcinoma cells microscopically, since individually separated malignant cells grow into the fibrous tissue without glandular formation. In this study, we used anti-scirrhous carcinoma monoclonal antibody S202, which reacted strongly with 100% of scirrhous gastric cancer samples, in order to evaluate the precise depth to which cancer cells invaded in the stomach wall. The invasive carcinoma cells could be detected more clearly by immunohistochemical staining with S202 than by histological staining with hematoxylin-eosin. Furthermore, S202 was more useful than anti-CEA (carcinoembryonic antigen) antibody.