Carcinoembryonic antigen (CEA) levels were determined in the peritoneal washings from 44 patients with gastric cancer to evaluate the usefulness for a predictor of postsurgical prognosis. Seventeen of the 21 patients (80.9%) with serosal invasion showed elevated levels of CEA, whereas most of the patients with no serosal invasion (22/23) showed low levels of CEA and did not develop peritoneal metastasis. All patients with positive cytology showed elevated levels of CEA in the peritoneal washings. Therefore, CEA levels in the peritoneal washings could be an adjunctive tool for predicting the postsurgical prognosis in gastric cancer.