Although causative factors are not completely defined, carcinogenesis of colorectal cancer is attributed to multiple genetic alterations. The abnormal expressions of oncogenes are regarded to be responsible for the production of malignant phenotype, subsequent invasion and metastasis. From 63 surgically resectable colorectal adenocarcinoma patients, expression of oncogenes in colorectal cancer tissue was evaluated with immunohistochemical staining methods using monoclonal antibodies to products of the oncogenes. To evaluate the possibility of oncogenes as a prognostic factor, we studied the relationship between the expression of oncogenes and the clinicopathologic findings which are well known prognostic factors. Rates of expression in colorectal cancer tissue were 27% for c-myc, 74.6% for c-Ha-ras and 77.8% for c-erbB-2 oncogenes. The positive rate of c-erbB-2 oncogene was higher in the well differentiated group than in the poorly differentiated group. The rates of expression of c-myc and c-Ha-ras oncogenes were significantly correlated each other. Expression of these oncogenes in colorectal cancer were not correlated with the pathologic stage, location of cancer, DNA ploidy pattern and histologic differentiation except between c-erbB-2 and histologic differentiation. In conclusion, there seems to be a possibility that c-erbB-2 could be used as a prognostic factor of colorectal cancer. However, further and more intensive study seems to be required.