Serum carcinoembryonic antigen (CEA) levels were determined preoperatively in 221 patients with well-differentiated gastric cancer. The mean preoperative serum CEA level was 15.9 +/- 88.5 ng/ml (1.0-1,133.0 ng/ml) for all patients, and the incidence of an elevated CEA (> 5 ng/ml) was 11.8% (26/221). The CEA-positive patients had larger tumors, a more prominent serosal invasion, more frequent lymphatic and vascular involvement, less expansive tumor growth and higher rates of lymph node and hepatic metastases than did the CEA-negative patients. Thus, the CEA-positive patients had a more advanced stage of disease, and 61.5% underwent noncurative resection (vs. 11.3% in CEA-negative patients). The survival rate of the CEA-positive patients was lower than that of the CEA-negative ones (p < 0.01). As the multivariate analysis revealed the preoperative CEA level to be an independent prognostic factor for survival, an assay for this antigen prior to surgery is to be recommended.