In order to establish an efficient gamma delta T cell-mediated immunotherapy for hematological malignancies, we attempted to evaluate cytotoxicity against tumor cells by gamma delta T cells, which were generated from blood cells of patients with myeloma and lymphoma by culturing with zoledronate and a low dose of IL-2. Although gamma delta T cells were expanded in patients with myeloma and lymphoma as well as normal persons, the amplification rates of gamma delta T cells before and after culturing varied from patient to patient in myeloma and lymphoma. gamma delta T cells generated in patients with myeloma and lymphoma showed a potent cytotoxic ability against myeloma/lymphoma cell lines as shown in gamma delta T cells generated in normal subjects. In addition, gamma delta T cells generated in a patient with myeloma showed a cytotoxic ability against self myeloma cells freshly prepared from bone marrow. However, the same gamma delta T cells were demonstrated to be non-cytotoxic to normal cells of the patient. These data demonstrated that gamma delta T cells, which could be expanded in vitro from blood cells of patients with myeloma and lymphoma by culturing with zoledronate and IL-2, possess a sufficient cytotoxic ability against tumor cells. These findings suggested that in vitro generated patients' gamma delta T cells could be applied to gamma delta T cell-mediated immunotherapy for hematological malignancies.