β-Galactosidase (GZ) is an intracellular protein that is frequently used to express cloned antigens as fusion proteins in Escherichia coli. Salmonella typhimurium strain SL3261, an attenuated aroA vaccine strain, was used as a carrier for the plasmid pXY411, which directs the expression of GZ in salmonellae (which do not normally produce this protein). The resulting strain—SL3261(pXY411)—expressed GZ as an intracellular antigen. The plasmid was stable in vitro and in vivo and did not significantly alter the behavior of strain SL3261 in mice. Animals intravenously vaccinated with this construct developed circulating antibodies to GZ, as measured by ELISA, and delayed hypersensitivity to the antigen injected in the footpad. These results indicate that attenuated salmonellae may be expected to elicit both humoral and cellular responses to intracellular cloned antigens.