Natural killer (NK) cells perform multiple biological functions including tumor cell lysis and eradicating virally infected cells. Here, we report for the first time that d-galactosyl-β1-1 ' sphingosine and d-glucosyl-β1-1 ' sphingosine damage human NK cells. We show that these cells express T-cell-associated gene-8, the receptor for glycosphingolipids. d-Galactosyl-β1-1 ' sphingosine and d-glucosyl-β1-1 ' sphingosine induce the in vitro chemotaxis of human NK cells. Both d-galactosyl-β1-1 ' sphingosine and d-glucosyl-β1-1 ' sphingosine inhibit the cytotoxicity and IFN-γ secretion by these cells. Further analysis shows that the glycosphingolipids d-galactosyl-β1-1 ' sphingosine and d-glucosyl-β1-1 ' sphingosine but not any other lipid examined, which include d-lactosyl-β1-1 ' sphingosine, sphingosine 1-phosphate, sphingosine, lysophosphatidic acid, and phosphatidic acid, induce the apoptosis, globoid-like formation, and multinucleation in human NK cells. These results may have important implications on diseases where glycosphingolipids accumulate.