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The aim of this research was to obtain a combined recombinant protein consisting of immunodominant regions of Brucella outer membrane proteins (Omps) with the molecular weights of 25 kDa (Omp25) and 31 kDa (Omp31). The search for candidate proteins was carried out using NCBI PubMed and NCBI GenBank databases. The two most immunodominant regions of Omps were selected. The first region was in a position from 48 to 83 amino acids of Omp31, while the second one was in the position from 180 to 224 amino acids of Omp25. This combined sequence was designated as OmpBm-Ba. The pET32 vector was used for cloning and the expression of the combined recombinant protein in E. coli BL21(DE3). The antigenicity of recombinant OmpBm-Ba (rOmpBm-Ba) as compared with rOmp25 and rOmp31 has been tested on the sera of 109 cattle with positive results to brucellosis according to classical serological tests. The rOmpBm-Ba had a higher antigenicity than the single ones, since it confirmed the presence of Brucella-antibody in all serum samples with positive results of i-ELISA/rOmp25 and/or i-ELISA/rOmp31, as well as additionally revealing 7.3% and 31.2% seropositive animals, respectively. A comparative study of the diagnostic value of i-ELISA/rOmpBm-Ba and conventional tests on blood sera of 24 cattle subjected to a bacteriological examination at slaughter showed a higher reliability of enzyme immunoassay. Further research is necessary to get a more objective evaluation of the diagnostic accuracy of Brucella rOmpBm-Ba by challenging laboratory animals. .