PURPOSE: Although the overall survival and recurrence rates after open or laparoscopic surgery for colorectal cancer are similar, the potential oncological benefits of laparoscopic surgery have not been established. This study compared the effects of the two surgical approaches (open and laparoscopic) on the intraoperative inferior mesenteric vein (IMV) carcinoembryonic antigen (CEA) levels in patients who were undergoing open or laparoscopic surgery for sigmoid colon and rectal cancer. METHODS: Between December 2005 and July 2008, a total of 37 patients were enrolled in this study. Twenty one patients underwent open surgery and 16 patients were operated on laparoscopically. The baseline peripheral CEA level was measured preoperatively. The IMV blood was taken before and after mobilization of the cancer-bearing bowel segment and the CEA levels in the two groups were compared. RESULTS: The baseline CEA levels in the peripheral vein were similar in the two groups. After mobilization, the overall CEA level was elevated. The median pre-mobilization CEA levels of the open and laparoscopic group were 2.3 (range: 1.2~3.7) ng/ml and 1.5 (range: 1.0~2.6) ng/ml, respectively. Hence, the degree of CEA elevation after mobilization was significantly higher in the open surgery group compared with that of the laparoscopic approach (4.2 vs. 1.6, respectively, p=0.004). CONCLUSION: The CEA levels measured from the IMV after mobilization were elevated to a lesser degree after laparoscopic mobilization of the cancer-bearing bowel segment, as compared with that of open surgery. However, the long term oncological effects need to be examined by conducting longer, larger scale studies.