The reaction of indirect hemagglutination with an antibody erythrocyte diagnosticum is one of the promising methods for identifying the causative agent of infectious diseases or antigen. This preparation has not yet been developed for the diagnosis of infectious epididymitis of rams. The results of the preparation of an antibody erythrocyte diagnosticum in the reaction of indirect hemagglutination for the detection of the causative agent of infectious epididymitis in various biological material are presented in the article. As a result of scientific research, authors developed the method for obtaining an original Brucella ovis antibody diagnosticum for the reaction of indirect hemagglutination by sensitizing sheep erythrocytes with hyperimmune Brucella ovis serum using alizarin blue indicator of the epididymitic pathogen or antigen in biomaterial as the conjugate. Studies have shown the specificity and higher sensitivity of the indirect hemagglutination reaction with the antibody erythrocyte diagnosticum, compared with the antibody neutralization reaction and the bacteriological method, and its suitability for the indication of Brucella ovis antigen in biomaterial and environmental objects. It was also found that the reaction of indirect hemagglutination with antibody diagnosticum is much faster than the reaction of neutralization of antibodies and the bacteriological method. Research to improve the diagnosis of infectious ram epididymitis caused by Brucella ovis has been completed with the development of the antibody erythrocyte diagnosticum for the indirect hemagglutination reaction.The high specificity and activity of this preparationwas established by the authors. As a result of the studies carried out to test the diagnostic value of the antibody diagnosticum, a higher sensitivity of the indirect hemagglutination reaction using the new antibody diagnosticum, compared with the neutralization reaction of antibodies and the bacteriological method, and the suitability of using the diagnosticum for the indication of the Brucella ovis antigen in biomaterial, was established, which meets the requirements for express methods for detecting antigens in pathological material.