Induction of anti-tumour immunity in syngeneic mice by LBC cell line derived from a non-immunogenic T cell leukaemia was studied. The immunization of BALB/c mice with LBC irradiated cells induced in them anti-tumour spleen cells, cytotoxic T lymphocytes and anti-LBC antibodies. The anti-LBC antibodies reacted with components of 14, 16 and 27 kDa present on LB tumour cells, LBC cell line and normal thymocytes, but not with normal lymph node cells. Furthermore, immunization of the autologous hosts with LBC cells partially protected them against subsequent challenge with the original LB leukaemic cells. These findings demonstrate that culture conditions induced modifications in the antigenic properties of the leukaemic cells, allowing LBC cells to stimulate an immune response directed against components expressed at early stages during T cell maturation. These results also suggest that the immune response is responsible for the prolongation of the survival time of the mice inoculated with the parental leukaemic cells.