OBJECTIVE: To identify factors in favor of tumor cell adherence to the peritoneum. METHODS: Pieces of peritoneum from BALB/c mice were collected and incubated in vitro in the presence of human gastric cancer MGC-803 cells. Cells adhered to the peritoneum was assessed by MTT staining. The result was expressed as the percentage of tumor cells adhered (AD). RESULTS: If the peritondum had been previously injured, either by scraping or exposure to air, AD was significantly more than that of the control (P < 0.01). AD was significantly increased as compared to the control when the peritoneum was cultured in the presence of white cells, platelets, plasma or CEA. CONCLUSION: Adhesion of cancer cells to the peritoneum may be facilitated by peritoneal injury, and the presence of normal blood constituents. Oncofetal antigen with adhesive property such as CEA also helps tumor cells adhere to the peritoneum. The likelihood of post-operative peritoneal metastasis can be minimized if care has been taken to protect the peritoneum from injury and to thoroughly wash the peritoneal cavity before the abdomen is closed.