The aim of the present study was to evaluate the possibility that measurement of gastric carcinoembryonic antigen(CEA) might be a better diagnostic aid, in the diagnosis of gastric carcinoma, than serum CEA. We measured simultaneously serum and gastric juice CEA in 115 patients (38 chronic gastritis, 12 benign gastric ulcer, and 65 gastric carcinoma) who were confirmed by endoscopic biopsy. Gastric juice CEA was more sensitive in the diagnosis of gastric carcinoma than serum CEA (65% vs. 17% positive). Gastric juice CEA was elevated in 32% of benign gastric diseases, 50% of early gastric carcinoma, and in 17% of advanced gastric carcinomas. No significant correlation was found between age, sex, location or grosstype of tumor and gastric juice CEA levels. We conclude that measurement of gastric juice CEA may be more sensitive, in the diagnosis of gastic carcinoma, than serum CEA. However, gastric juice CEA seems to be not helpful for distinguishing between benign and malignant lesions, and thus this subject should be studied further for screening high risk patients, for identifying and following patients with premalignant conditions, and for following cancer patients before and after treatment.