The immunohistochemical expressions of the apoptosis-related proteins Bcl-2, Bcl-xL/S, Bax and Bak were investigated in tumor specimens selected from 58 consecutive patients undergoing surgery for advanced colorectal carcinoma. The expression patterns in 50 specimens of adjacent normal colonic mucosa were also examined. In the normal colonic mucosa, Bcl-2-positive epithelial cells tended to be located at the base of the crypts, while the Bcl-xL/S-, Bax- and Bak-positive epithelial cells tended to be located at the luminal surface. The intracellular expression patterns of Bcl-2 and Bax were diffuse cytoplasmic, whereas those of Bcl-xL/S and Bak were granular cytoplasmic. In the adenocarcinomas, the intracellular expression patterns of all antibodies were diffuse cytoplasmic, and the percentages of Bcl-2-, Bcl-xL/S-, Bax- and Bak-positive cases (>20% of cancer cells labeled) were 29%, 43%, 45% and 69%, respectively. Bax expression was significantly correlated with less lymph vessel invasion (p=0.02) and less depth of invasion (p=0.04). In relation to prognosis (5-year-survival), the patients with Bax-positive tumors had significantly better prognoses than the patients who had Bax-negative tumors (p<0.05). However, the Bcl-2, Bcl-xL/S and Bak expressions were not related to any clinicopathological factors examined. Thus, Bax expression may be an additional prognostic marker in colorectal carcinomas.