Carcinoembryonic antigen (CEA) was quantified pre- and post-operatively in plasma from 171 patients with gastric carcinoma. The pre-operative plasma concentration was above the normal reference value (3.5 micrograms/l) in 18% of the patients in stage I-III (pTNM) and in 57% of the patients in stage IV. Pre-operative concentrations above 10 micrograms/l indicated metastatic or inoperable disease. The concentrations were not different between the stages I, II and III. However, the pre-operative CEA concentrations were related to survival after potentially curative resection. At recurrence most of the patients had markedly increased CEA, often with increasing CEA in the months before clinical recurrence. Most of the patients clinically disease-free at the end of the follow-up period had a transitory or prolonged post-operative elevation of CEA. This made the post-operative evaluation of CEA difficult. Serial determination of CEA in the follow-up of gastric cancer patients therefore had little or no clinical value, whereas the pre-treatment levels were of clinical significance.