Human Vγ9Vδ2 T cells recognize phosphorylated nonpeptide Ags (so called phosphoantigens), certain tumor cells, and cells treated with aminobisphosphonates. NKG2D, an activating receptor for NK cells, has been described as a potent costimulatory receptor in the Ag-specific activation of γδ and CD8 T cells. This study provides evidence that Vγ9Vδ2 T cells may also be directly activated by NKG2D. Culture of PBMC with immobilized NKG2D-specific mAb or NKG2D ligand MHC class I related protein A (MICA) induces the up-regulation of CD69 and CD25 in NK and Vγ9Vδ2 but not in CD8 T cells. Furthermore, NKG2D triggers the production of TNF-α but not of IFN-γ, as well as the release of cytolytic granules by Vγ9Vδ2 T cells. Purified Vγ9Vδ2 T cells kill MICA-transfected RMA mouse cells but not control cells. Finally, DAP10, which mediates NKG2D signaling in human NK cells, was detected in resting and activated Vγ9Vδ2 T cells. These remarkable similarities in NKG2D function in NK and Vγ9Vδ2 T cells may open new perspectives for Vγ9Vδ2 T cell-based immunotherapy, eg, by Ag-independent killing of NKG2D ligand-expressing tumors.