Intraperitoneal chemotherapy has been the treatment for peritoneal seedings. Most of the anti-tumor agent administered intraperitoneally is absorbed from visceral peritoneum, gets into the portal vein system and reaches the liver. Theoretically, intraperitoneal administration of anti-tumor agents must show equivalent effects on the liver metastasis to portal vein infusion. We compared the efficacy of intraperitoneal and intravenous administration of 5-FU, CDDP and CPT-11, using colon 26 mouse liver metastasis model. Intraperitoneal administration of 5-FU or CPT-11 was statistically superior to intravenous administration to diminish the liver metastatic deposits. CDDP experiment did not show a statistical difference, but the superiority intraperitoneal administration was recognized. Intraperitoneal administration of anti-tumor agents is more effective for not only peritoneal seedings but also liver metastases than intravenous administration. Intraperitoneal chemotherapy might be an effective adjuvant chemotherapy for gastrointestinal malignancies.