 We are undertaking a study of patients with gastric or pancreatic cancer. A common place for cancer to return after surgery for gastric or pancreatic cancer is the inside lining of the abdomen, called peritoneal metastasis. At the time of surgery, washing the abdomen with a mild salt solution may reveal free cancer cells in the abdomen which could develop into peritoneal metastasis. Recently, surgeons here at Memorial Sloan-Kettering have found that patients who have these cells develop peritoneal metastases and are better treated with chemotherapy rather than surgery. Sometimes, though, these cells might be present but cannot be found by using current techniques. We are trying to figure out a better way to find these free cancer cells. This could improve our treatment of patients with gastric and pancreatic cancer. We need negative control population to which we can compare the peritoneal washings of these cancer patients. 