In an attempt to identify the mechanisms by which the carcinoembryonic antigen (CEA) of gastric cancer tissue origin is secreted into the sera, we determined CEA positivity in tissues and sera of individual patients and compared these data with tumour size, histological classification, postoperative staging, grading, and survival times. CEA was demonstrated in tissues of 93 patients by the indirect immunoperoxidase technique and in sera of 83 patients by an enzymoimmunoassay. CEA was found in 96% of the tumours with the highest intensity of staining in signet-ring cell carcinomas. 25% of patients had elevated serum levels ( > 5.0 ng/ml). Serum levels were clearly influenced by tumour stage, tissular staining intensity and tumour size, but not by histological classifications or tumour grade. Stage III and IV patients with elevated CEA serum levels had a significantly lower survival time (p = 0.0046) than patients with normal levels. These observations are only partly valid for signet-ring cell carcinomas, for which CEA serum estimations are of limited value.