P120cas is involved in signal transduction upon src or growth factor stimulation as well as in E-cadherin mediated cell adhesion and may play an important role in carcinogenesis. In this study, we evaluated immunohistochemically the expression and cellular localization of p120cas in 40 gastric, 43 colorectal and 20 pancreatic carcinomas, and examined the relationship between p120cas expression and pathological features. Altered p120cas expression was observed in 70%, 65% and 60% of gastric, colorectal and pancreatic cancers, respectively. The most common abnormality was of cytoplasmic expression associated with loss of membranous distribution found in 37% of gastric, in 25% of colorectal and in 25% of pancreatic cancers. Heterogeneous staining was noted in 15%, 19% and 20%, and complete loss of expression in 18%, 21% and 15% of gastric, colorectal and pancreatic cancers, respectively. There was no correlation between p120cas staining pattern and tumour grade or stage. Aberrant expression of p120cas which may reflect changes in signal transduction pathways occurs frequently in human malignancies.