Malignant transformation is associated with abnormal glycosylation, resulting in the synthesis and expression of altered carbohydrate determinants including sialyl Lewis^a and sialyl Lewis^x. The sialyl Lewis^a and sialyl Lewis^x determinants appear in the sera of patients with cancer, and are extensively utilized for serum diagnosis of cancers in Japan. Sialyl Lewis^a and sialyl Lewis^x are involved in selectin‐mediated adhesion of cancer cells to vascular endothelium, and these determinants are thought to be closely associated with hematogenous metastasis of cancers. Recent progress in this area includes the following: 1. Substantial increases in solid clinical statistics that further confirm the contribution of these determinants in the progression of a wide variety of cancers; 2. Elucidation of the ligand specificity of the three family members of selectins and evaluation of the roles of these molecules in cancer cell adhesion; and 3. Advances in the study of the mechanism that leads to the enhanced expression of the sialyl Lewis^a/x determinants in malignant cells. These recent results have confirmed that these determinants are not merely markers for cancers, but are functionally implicated in the malignant behavior of cancer cells. The results also suggested that the increase of these determinants in malignant cells is an inevitable consequence of the malignant transformation of cells. Considerable new knowledge has also been accumulated regarding the therapeutic implications for suppression of hematogenous metastasis targeting this cell adhesion system.