We used a retroviral shuttle vector [pZIPNeoSV(X)] to transfect a monocyte-like murine tumour cell line (J774.G8) with the Mycobacterium leprae gene encoding heat-shock protein (hsp) 65. The antigen was expressed and presented on the surface of the transfected cell in association with major histocompatibility complex (MHC) class I and class II for recognition by T cells from specifically sensitized mice. We show here that when these transfected cells were used as a vaccine and introduced parentally into syngeneic (BALB/c) mice they conferred a remarkably high degree of protective immunity against subsequent challenge with either M. bovis bacillus Calmette-Guérin (BCG) or M. tuberculosis H37Rv.