Gamma/delta T cells (Vgamma9delta2) contribute to innate immunity and exert natural cytotoxicity against a variety of tumors. Using a synthetic phosphoantigen (Bromohydrin Pyrophosphate, BrHPP), we amplified Vgamma9delta2 T cells in vitro from neuroblastoma patients. In the presence of BrHPP and low doses of IL-2, robust proliferation of Vgamma9delta2 T cells was obtained from peripheral blood mononuclear cells (PBMC) harvested at diagnosis. Moderate proliferation was observed from PBMC harvested after stem cell transplantation, whereas modest levels of Vgamma9delta2 T cells were obtained from PBMC harvested after induction therapy. Proliferation was observed after a single in vitro stimulation with BrHPP. After 21 days in culture, Vgamma9delta2 T cells represented more than 80% of cultured cells (a 50-fold expansion from baseline). Moreover, BrHPP-amplified Vgamma9delta2 T cells from patients-expressed activation markers and were able to lyse allogeneic and autologous neuroblasts. This cytotoxic activity was gammadelta T-cell receptor-dependent. Clinical trials using BrHPP are warranted in patients with poor-prognosis neuroblastoma, either to expand patient-derived Vgamma9delta2 T cells ex vivo or by direct administration to in vivo to boost the pool of resident Vgamma9delta2 T cells in vivo.