In the last 5 years significant progress has been made in our understanding of the molecular nature of anti-tumour T cell-mediated responses. This review describes the involvement of the cellular immune system in the recognition and destruction of cancer cells. Four aspects are discussed: (i) the generalized immune activation induced by the systemic administration of cytokines, in particular, interleukin-2; (ii) the specific T cell-mediated reactions against tumour cells through the recognition of tumour-associated molecules, 1) and tyrosinase proteins described in melanomas, and minor histocompatibility antigens in the setting of allogenic bone marrow transplantation for leukaemia; (iii) the potentially significant but still hypothetical immune-mediated recognition of molecules either tumour-associated or transformation-related (including altered oncogenic proteins); and (iv) the role of co-stimulatory molecules in the induction of tumour-specific immunity. The current and future therapeutic applications in cancer treatment and potential limitations in this approach are discussed.