From tumors obtained from 87 patients with colorectal cancer during operation, portal blood levels of carcinoembryonic antigen (CEA) in drainage vein were measured and evaluated, according to the disease stage and histology, in comparison with cancerous tissue CEA in the extracts of surgical specimens and immunohistochemical analyses graded according to localization patterns and immunoreactivity; thereby trying to clarify a mechanism for the elevation of peripheral CEA levels. Mean value of portal CEA was higher than that of peripheral CEA at each stage of diseases, with a marked elevation by operative procedures. Although no significant correlation was observed between CEA contents of cancerous tissue (ng/g wet weight) and peripheral CEA levels, a close correlation was observed between portal CEA levels and cancerous CEA contents. A high CEA value was noted in moderately differentiated adenocarcinoma, according to cell differentiation (p less than 0.05). High portal CEA level was recognized in those with stain of cytoplasm and stroma, besides cancerous tissue CEA content, by means of immunopathochemical localization pattern, but a more significantly elevated CEA level was observed in those with the cancer pathologically infiltrating over muscle layers. The present study suggests that the route of CEA transfer from tumor to portal blood can be an important contributing factor to the control of peripheral CEA level.