The serum levels of sialyl Lewis(a) (CA19-9), sialyl Lewis(x) (SLX), sialyl Tn (STN) and carcinoembryonic antigen (CEA) in peripheral venous blood and tumor drainage venous blood of colorectal cancer patients were examined to determine their value as prognostic factors after surgery. Blood samples were obtained from the peripheral vein and from the tumor drainage vein from 124 colorectal cancer patients during surgical excision of the tumor. The patients were divided into high-antigen and low-antigen groups for each antigen in each location. Serum levels of SLX, STN and CEA in tumor drainage venous blood (d-SLX, d-STN and d-CEA, respectively) were significantly higher than in peripheral venous blood (p-SLX, p-STN and p-CEA, respectively). The survival time after surgery for patients with high d-SLX or d-CEA levels and low levels of the same antigen in peripheral venous blood was significantly shorter than the survival time for those patients with low levels of antigen at both sites (p = 0.0003 or p = 0.0406, respectively). Cox's regression analysis revealed that a high d-SLX or high d-CEA level was an independent prognostic variable for patient survival. In conclusion, determining d-SLX or d-CEA is more useful than p-SLX or p-CEA in predicting the outcome for colorectal cancer patients.