To evaluate the preventive potential of intraoperative or early postoperative local administration of peptide PIII into the abdominal cavity against peritoneal carcinomatosis.Human gastric cancer cells of the line GC9811 were inoculated subcutaneously into nude mice to cause subcutaneous carcinoma. The 8th generation cancer was taken out to isolate the cancer cells to be inoculated into the serous membrane at the greater curvature of the stomach. Forty-eight nude BALB/C-nu/nu mice underwent implantation of the 8th generation cancer cells into the serous membrane at the greater curvature of the stomach via minilaparotomy so as to establish models of peritoneal carcinoma The 48 mice were randomly divided into 3 equal groups: Group 1 (control group); Group 2, undergoing intraperitoneal perfusion of 100 microg of peptide PIII, and post-operative intraperitoneal perfusion of 2 mg/kg peptide PIII twice; and Group 3, undergoing post-operative intraperitoneal perfusion of 100 microg/kg peptide PIII twice. Six mice in every group were sacrificed on the day 23 to undergo pathological examination. The other mice in every group were used to evaluate the survival rate. The tumor-bearing mice showing manifestations of failure were killed to undergo pathology.The weight of individual tumor was not significantly different among the 3 groups. The number of peritoneal metastatic nodules of Group 2 was (9.2 +/- 1.3), significantly less than those of Group 1 and 3 [(126.3 +/- 9.6) and (64.2 +/- 8.3) respectively, both P0.01]. The number of metastatic nodules2 mm of Group 2 was 1.6 +/- 0.2, significantly less then those of Groups 1 and 3 [(51.2 +/- 3.6) and (21.7 +/- 4.9) respectively, both P0.01]. The survival rate of Group 2 was significantly longer than those of Groups 1 and 3 (both P0.01).Peptide PIII does not significantly inhibit the growth of GC, but significantly reduce the peritoneal metastasis of GC. An ideal targeting chemotherapy, intra-operative application of peptide PIII into the abdominal cavity plus intraperitoneal perfusion is an attractive and promising strategy to prevent peritoneal metastasis of GC.