T lymphocytes are often induced naturally in melanoma patients and infiltrate tumors. Given that gamma delta T cells mediate antigen-specific killing of tumor cells, we studied the representation and the in vitro cytokine production and cytotoxic activity of tumor infiltrating gamma delta T cells from 74 patients with primary melanoma. We found that gamma delta T cells represent the major lymphocyte population infiltrating melanoma, and both V delta 1(+) and V delta 2(+) cells are involved. The majority of melanoma-infiltrating gamma delta cells showed effector memory and terminally-differentiated phenotypes and, accordingly, polyclonal gamma delta T cell lines obtained from tumor-infiltrating immune cells produced IFN-gamma and TNF-alpha and were capable of killing melanoma cell lines in vitro. The cytotoxic capability of V delta 2 cell lines was further improved by pre-treatment of tumor target cells with zoledronate. Moreover, higher rate of gamma delta T cells isolation and percentages of V delta 2 cells correlate with early stage of development of melanoma and absence of metastasis. Altogether, our results suggest that a natural immune response mediated by gamma delta T lymphocytes may contribute to the immunosurveillance of melanoma.