A recombinant plasmid pEK6 determining the synthesis of a hybrid protein the N-terminus of which was represented by full-size beta-galactosidase and C-terminus by HIV-1 gene env virus-specific sequence was constructed. The analysis of lysates of E. coli HB101/pEK6 bacteria in 6% PAAGE revealed additional proteins with molecular weights from 185 to 130 kDa. These proteins interacted with blood serum antibodies of a virus carrier but formed no specific bands with sera from normal donors. Densitometric analysis of polyacrylamide gels stained with Coomassi R250 demonstrated that the level of production of recombinant protein was at least 15% of the total cell protein. Hybrid polypeptides formed poorly soluble inclusion bodies in the bacterial cells. Study of the immunological properties of the recombinant polypeptides showed that immunization of rabbits with these proteins induced antibodies specifically reacting with viral polypeptides with molecular weights of about 82 and 140 kDa. Such features as a high level of synthesis, technologically feasible purification of inclusion bodies, and adequate antigenic properties recommend this preparation for use in the development of diagnostic test systems.