Studies in epithelial cancer, including colorectal cancer, suggest that c-erbB-2 may be an important gene in metastatic disease. The expression of c-erbB-2 mRNA and c-neu were assessed in 25 human non-metastasising colorectal cancers and 34 primary metastasising colorectal cancer and their liver metastasis by in situ hybridisation and immunohistochemistry respectively. The metastasising colorectal cancers and their liver metastases expressed c-erbB-2 mRNA (76%, 70%) and c-neu (70%, 68%) at significantly higher levels than the nonmetastasising tumours (28% and 36% respectively chi-squared: p < 0.003 and p < 0.04). Moreover, c-erbB-2 mRNA predicted the development of liver metastases in tumours that had not metastasised to lymph nodes (p = 0.002). This gene may play an important role in the development of metastasis in colorectal cancer and its mRNA expression may have important implications for deciding which patients with lymph node negative disease require chemotherapy.