A set of recombinant plasmids containing different fragments of HTLV-I env gene has been constructed on the basis of pUR290-pUR292 vectors. The hybrid proteins containing different fragments of ENV predecessor in the C-terminal of beta-galactosidase differed in stability in Escherichia coli cells. The presence of N-terminal of ENV predecessor in recombinant proteins considerably decreases their resistance to proteases of the bacterial cell. Elimination of this fragment led to obtaining of the recombinant plasmid pESG coding for the high level of synthesis of the env-specific hybrid polypeptide (up to 30% of the total cellular protein). This 134 Kda protein is able to interact efficiently with the HTLV-I positive sera and may be used in the diagnostic test-systems for identification of the HTLV-I infected patients.