The capacity of a previously described plasmid vector pAZ to deliver bioactive proteins to targets in vivo has been studied. This vector molecule has a strong constitutive promoter, is extremely stable in cells of vaccinal S. choleraesuis strain, and encodes the synthesis of marker protein beta-galactosidase which helps monitor the vector's fate in the host. The gene encoding hepatitis B virus core antigen (HBcAg) has been inserted into pAZ under its constitutive promoter. The resultant recombinant plasmid p19-24 has been used to transform Enterobacteriaceae (E. coli and S. choleraesuis) cells. Transformed cells produce immunologically active HBcAg. p19-24 was stable in S. choleraesuis cells during their culturing and during this strain persistence in mice. Triple oral immunization of rabbits in a dose of 1 x 10(9) S. choleraesuis cells TC177 induced the production of virus-specific antibodies. Successful transformation of cells of another vaccinal strain S. abortus ovis by this plasmid extends the potentialities of the vector. The results demonstrate good prospects of using pAZ vector for the construction of live oral vaccines.