In order to ascertain the role of gastric carcinoembryonic antigen (CEA) determination in detecting patients with a risk for gastric cancer, 69 subjects were studied; 23 were referred for endoscopy because of dyspepsia but without obvious macroscopic lesions, 27 with duodenal ulcer, 11 with benign gastric ulcer, 8 with gastric cancer. The following results were obtained by subdividing the material according to the histologic interpretation of the results of gastric mucosal biopsies: (1) in the presence of minor histologic abnormalities of the gastric mucosa, CEA in gastric juice was under 100 ng/ml in all but five cases; and (2) in moderate or severe chronic atrophic gastritis (associated or otherwise with intestinal metaplasia or dysplasia), and in gastric cancer, gastric CEA ranged between 224 and 3120 ng/ml in all but two cases. Although not diagnostic for gastric cancer, gastric CEA is a promising test in detecting patients at risk, including those with dysplasia of the gastric mucosa.