Carcinoembryonic Antigen is one of most frequent.ly checked tumor markers in cancer management. We performed statistical analysis with serum CEA data of 2626 persons who received regular health examination and were thought to be free of active disease to determine the cutoff values of serum CEA level in normal Korean adults and to study the factors influencing serum (:EA levels in normal subjects. 1) The cutoff values of serum CEA in normal Korean adults in general were 9.28ng/ ml for men, 5.90 ng/ml for women. 2) Serum CEA level was influenced by age, present smoking history, sex, and abnormal findings in chest X ray. 3) Serum CEA level had no correlation with the history of amount of alcohol consumption or obesity. 4) Cutoff values of serum CEA in normal Korean adults were tabulated according to age, sex, and smoking histor y. Serum CEA level was influenced by age, sex, present smoking history and abnormal findings in chest X ray and cutoff values of serum CEA were tabulated according to age, sex, and smoking history.