To evaluate clinical importance of the expression of sialyl Lewis-X (sLe(x)) and sialyl Lewis-a antigen (sLe(a)) in gastrointestinal cancers, we examined immunohistochemically expression of the two antigens in esophageal, gastric, colorectal, and pancreatic cancer. Expression of sLe(x) and sLe(a) were associated with several clinicopathologic features which reflect tumor aggressiveness in esophageal, gastric and colorectal cancer, but not in pancreatic cancer. In esophageal and colorectal cancer, survival rate of the patients with sLe(x) positive tumors was significantly poorer than that of the patients with sLe(x) negative tumors, while in gastric cancer that with sLe(a) positive tumors was significantly poorer than that with sLe(a) negative. Cox's multivariate analysis revealed that sLe(x) expression status was one of the significant discriminants of prognosis in colorectal cancer patients and sLe(a) status in gastric cancer patients. These results suggest that sLe(x) and sLe(a) expression could be involved in aggressiveness of gastrointestinal cancer and might prove to be a potent marker for prognosis in patients with gastric cancer and colorectal cancer.