['Little is known about the role of the CO2 pneumoperitoneum on tumor cells that spread from the portal system into the liver during laparoscopic surgery for gastrointestinal malignancies. Therefore, we designed a study to investigate the effect of CO2 pneumoperitoneum on cancer cells implanted in the portal vein in a rabbit model.', 'Immediately after intraportal inoculation of 2.5x10(5) cells of VX2 cancer, the rabbits received either CO2 pneumoperitoneum at a pressure of 10 mm Hg for 30 min (pneumoperitoneum group, n = 14) or laparotomy alone for 30 min (laparotomy group, n = 14).', 'The number (p<0.01) and area of cancer nodules (p = 0.045) on the liver surface on day 17 were greater in the pneumoperitoneum group than in the laparotomy group. The frequency of cancer nodules >3.0 mm in diameter was higher in the pneumoperitoneum group than in the laparotomy group (p<0.001).'] Does pneumoperitoneum with carbon dioxide enhance liver metastases of cancer cells implanted into the portal vein in rabbits?