The candidate malarial vaccine epitope, region II of Plasmodium falciparum circumsporozoite protein (RII-CSP), was cloned into Mycobacterium smegmatis and M. bovis BCG via a mycobacterial replicative plasmid pUS1762. This plasmid contained a gene for the M. leprae 18 kDa protein to provide expression signals. Transformation was achieved by electroporation and selection for kanamycin resistance and verified by Southern hybridisation and sequencing. The transformation efficiency was in the order of 10(4) cfu/mg DNA for M. smegmatis and 10(3) cfu/mg DNA for M. bovis BCG. Western blotting using a polyclonal antibody specific for the RII-CSP and a monoclonal antibody specific for the M. leprae protein showed the expected 25 kDa band of the 18 kDa-RII-CSP fusion protein.