The CEA (carcinoembryonic antigen) was discovered in the blood of the patient in the colon cancer by Gold and Freedmann, (1965). Subsequent development of radioimmunoassay by Thomson et al (1969) made it possible to detect the very low concentrations of CEA in circulating blood, other body fluids and also in normal, benign and malignant subjects. Recently, the serum CEA levels is used as complementary diagnostic method and therapeutic indicators malignant patients, especially colorectal cancers. The authors detected CEA in serum by empolying sandwitch solid-phase radioimmunoassay of 22 normal controls, 51 of various benign diseases and 60 of various malignant diseases during period of 7 months from Fefruary to August, 1981 in Korea University Hospital. The results were as follows: 1. In the 22 cases of control group, the mean value of serum CEA was 1.62$pm$0.66ng/ml.) 2. In the 51 cases of benign diseases, the mean value of serum CEA was 4.53$pm$2.54ng/ml. (P value less than 0.005) 3. In the 60 cases of malignant diseases, the mean value of serum was 13.6$pm$11.25ng/ml. (P value less than 0.005) 4. In the 5 cases of liver metastasis, the mean value of the serum CEA levels were very high as compared with primary hepatic carcinoma.