The expression of p53 in colorectal tumors was studied immunohistochemically by monoclonal antibody (PAb1801). No nuclear staining was evident in the tumor cells of colorectal adenomas. p53 immunoreactivity was found in 59 (61.5%) of 96 colorectal cancers. There was no significant correlation between the p53 immunoreactivity and histologic type, tumor size, invasion of bowel wall, lymphatic invasion, venous invasion, lymph node metastasis, peritoneal dissemination, or liver metastasis. However, the p53 negative tumors showed a recurrence rate of 3.3%, while for the p53 positive tumors a recurrence rate of 20.9%. p53 negative tumors were associated with favorable prognosis, whereas those with p53 positive tumors were related to poor prognosis. DNA polymerase alpha positive cells rate in p53 positive tumors was significantly higher than in p53 negative tumors. The results suggested that p53 immunoreactivity might possibly be a useful prognostic marker of colorectal cancers.