Sialylated Lewis(x) and sialylated Lewis(a) antigens, which are structural isomer each other, were serologically tested to determine the clinicopathological differences and correlation between two antigens, and were also compared with those of serum CEA in 141 patients with gastric cancer. Percent positives in sialylated Lewis(a), CEA and sialylated Lewis(x) showed 26.9%, 21.8% and 17.0% respectively. Percent positive of sialylated Lewis(x) correlated with degree of liver metastasis and peritoneal dissemination. Therefore, it is emphasized that the role of sialylated Lewis(x) is characteristics of detecting a presence of liver metastasis and/or peritoneal dissemination. On the other hand, sialylated Lewis(a) showed high percent positive in cases which had lymph nodes metastasis and mucinous or papillary adenocarcinomas. These two carbohydrate antigens indicated no correlation (r = 0.062) in the spectrum of sera. It is suggested that combination assay of sialylated Lewis(x) and sialylated Lewis(a) is useful in detecting many gastric cancer patients including CEA-negative one.