BACKGROUND: Correlations between the AFP, CEA, CA19-9, and CA125 levels of portal and peripheral blood were examined in 42 patients (male, 29; female, 13; mean age, 55.9) with gastric cancer in order to identify a better blood sample for measuring these tumor markers. METHODS: The levels of these tumor markers were measured by the immunoradiometric assay. The cut-off levels of positivity were 6 ng/ml for AFP, 7 ng/ml for CEA, 25 U/ml for CA19-9, and 35 U/ml for CA125. RESULTS: The positive rates of AFP, CEA, CA19-9, and CA125 were 11.9%, 19.0%, 14.3%, and 7.1% in portal blood and 9.5%, 19.0%, 14.3%, and 4.8% in peripheral blood, respectively. The positive rate of portal venous CEA was significantly higher in cases with lymph node metastasis, distant metastasis, and lymphatic invasion than those without these variables. The positive rate of peripheral venous CEA was significantly higher in cases with lymph node metastasis, distant metastasis, high stages, and large tumor size. The positive rate of peripheral venous CA19-9 was higher in cases with distant metastasis. The positive rate of CA125 in portal and peripheral blood was higher in cases of lymphatic invasion. Neither portal nor peripheral AFP correlated with pathologic factors. Regression analysis revealed that the portal venous levels of AFP, CEA, CA19-9, and CA125 could be estimated by using the peripheral venous levels of these tumor markers. CONCLUSION: We can avoid intraoperative sampling of portal blood to measure the portal venous levels of AFP, CEA, CA19-9, and CA125 because the peripheral venous level of these tumor markers reflects the portal venous levels. The measurement of peripheral venous levels of CEA and CA19-9 can be used as non-anatomical prognostic indicators for staging of gastric cancer.