EN
Sera from 122 adult bulls and 1197 females aged between 1/2 and 17 vears were examined. The herds, their farms and regions were free from brucellosis, and the cattle were not vaccinated with Brucella Buck 19. All the sera showing titre ≤ 12.5 IU in the tube agglutination test (SAT) were negative after treatment with mercaptoethanol. Beginning from the SAT titre of 25 IU, the number of the mercaptoethanol test titres to be disclosed increased with a rise of the SAT titre. Out of 1319 animals examined altogether, the ME test titre was determined only in 2.2 per cent of the cases, but with sera of the SAT titre ≥ 25 IU - in 12.8 per cent. Depending on the SAT titre, mercaptoethanol caused the serum titre decrease by 1-3 dilutions, and the titre drop proved to be the highest at the SAT titre of 100 IU.