Peripheral γδ T cells derived from healthy donors were found to exhibit cytotoxicity against a variety of tumor cell lines in vitro, including CNE2, which was established from nasopharyngeal carcinoma (NPC). The anti‐tumor effects were further studied in a mouse model. Control nude mice inoculated s.c. with 5 × 10⁶ CNE2 cells regularly developed hypodermal tumors, which progressively increased in size, and animals had a mean survival of 35 ± 3.4 days. Tumor growth was arrested and tumor size was reduced after animals were infused with 5 × 10⁷ γδ T cells derived from a healthy donor. The anti‐tumor effects were temporary, however, and tumor growth was resumed after about 1 week in a group of the animals that had been given a single dose of γδ T cells. In another group of animals given 2 doses of γδ cells 1 week apart, resumption of tumor growth was delayed for a further week. Mean survival of the 2 groups was increased to 61 ± 15.7 and 74 ± 12.9 days, respectively. Immunohistology revealed an accumulation of infused cells in tumors attended by focal tumor necrosis in specimens taken 2 days after infusion. Infiltrative cells virtually disappeared from tumor tissues 6 days after infusion, accompanied by increased mitotic indices of tumor cells. These temporal relationships suggested that the accumulation of infused γδ T cells in hypodermal tumors was responsible for the observed anti‐tumor effects. © 2001 Wiley‐Liss, Inc.