THE concept of tumour surveillance implies that specific and nonspecific components of the immune system eliminate rumours in the early phase of malignancy(1,2). The immunological mechanisms that control growth-of preneoplastic cells are, however, not known. T cells expressing gamma delta T-cell receptors (TCR) were first described as lymphocytes with reactivity against various tumour cells, which suggests that gamma delta T cells could mediate tumour surveillance(3-6). Here we show that TCRV gamma 1.1J gamma 4C gamma 4 transgenic mice(7) are spontaneously resistant to acute T-cell leukaemias but cannot reject non-haematopoietic tumours. TCRV gamma 1.1J gamma 4C gamma 4(+) hybridomas isolated from these mice react in vitro against almost all haematopoietic tumour cell lines tested. Recognition of tumour cells depends on the gamma delta TCR but is independent of major histocompatibility complex (MHC) class I, MHC class II, or TAP-2 peptide transporter expression. Ligand recognition is influenced by the murine Nromp gene, which confers resistance or susceptibility to tuberculosis, lepra and leishmaniasis(8,9). These data indicate that TCRV gamma 1.1(+) T cells confer spontaneous immunity against haematopoietic rumours in vivo and link innate resistance to bacterial infections with tissue-specific tumour surveillance by gamma delta(+) T cells.