Background: A new tumor marker, TAG-72 has been identified using monoclona] antibody B72.3. It is found in a wide variety of carcinomas but rarely expressed in normal adult tissue and benign lesions. Methods: The presence of TAG-72 in serum samples from patients with gastric carcinoma and benign gastrointestinal disease has been evaluated using the CA72-4 assay. Results: Elevated levels of serum TAG-72 antigen were found in 25(39.1%) of 64 gastric carcinoma patients and none of 32 benign gastrointestinal disease patients. The serum concentrations of TAG-72 were compared to those of CEA. The positive rate of CEA in gastric carcinoma and benign gastroin- testinal disease patients were 37.5% and 9.4%, respectively. These results indicate a preferential expression of TAG-72 compared to CEA in gastric carcinoma patients versus in patients with benign disorder. Combinatinn assay using CA72-4 and CEA RIAs unchanged positive rate(50%, p 0.05). In patients with the more advanced stage of gastric carcinoma revealed the higher positive rate of serum CA72-4 and the levels were increased in all patients with recurrent gastric carcinomo. Conclusions: These results suggest that the measurement of serum CA72-4 in patients with gas1ric carcinoma serve as a complementary role to differentiate the disease from benign gastric lesions and may be useful to predict tbe disease recurrence in postoperative patients. (Korean J Gastroenterol 1996; 28:493 - 501)