Abstract Brucellosis is an infectious disease caused by different species of Brucella. These microorganisms cause disease in many different vertebrates. Pigs, cattle, goats, sheep and many kinds of wild animals are susceptible to Brucella infection. In Iran, brucellosis is a notifiable disease. While bacteriological isolation is the most specific diagnostic test, the frequency of isolation is usually low, and results are not available immediately. For this reason, many serological tests have been developed for the rapid diagnosis of brucellosis. Agglutination tests, Complement Fixation Tests and ELISA’s are most widely used for screening or confirmation. In the present study, one hundred and four blood samples were collected from aborted cows in different trimester of pregnancy from different industrial dairy herds in Mashhad, Iran. The blood samples were centrifuged at 2000 × g at room temperature for five minutes to separate sera. Serum samples were stored at -20ºC until used. Serum antibodies were tested by indirect ELISA. The results of antibody detection by indirect ELISA showed that out of 104 serum samples, 8 samples were positive. These cows had been vaccinated against brucellosis between 3-6 months of age. From these positive samples, 5 (% 4.80) and 3 (% 2.88) samples were related to the second and third trimester of pregnancy, respectively. From 8 seropositivesamples in aborted cows, 1 (% 0.98) sample was positive of Brucella abortus in culture.

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