The presence of the EF-hand-calcium-binding protein S 100A4 in the carcinoma cells of the primary tumour is associated with a shorter survival time of a group of breast cancer patients. In colon cancer, primary tumours as well as metastases to the liver can be studied. Here we show, using quantitative PCR applied to RNA from 24 normal colon, four liver tissues. 24 colon carcinoma specimens, and 24 livers containing colonic carcinoma metastases, that the level of S 100A4 mRNA was significantly higher in the carcinomas compared to normal specimers (Mann-Whitney U-test, P=0.05), and in liver metastases compared to carcinoma specimens (P=0.039). The latter comparison included seven liver metastases and their matched primary carcinomas (P < 0.001) from the same patient. In situ hybridization and immunocytochemistry techniques have localized S 100A4 to both carcinoma cells and lymphocytes in the malignant specimens. The percentage of specimens stained for S 100A4 in the epithelial cells is significantly higher for those isolated from carcinomas and metastases than from the corresponding normal tissue, and from metastases than from corresponding carcinoma (Fisher Exact text, P < 0.0016, P=0.04, respectively). In most specimens, S 100A4 is present in clusters of T lymphocytes and this distribution is also found in the lymphoid, uninflamed appendix.