Objectives: Avian influenza is an important respiratory disease of birds with great impact on poultry industry. Several serological and molecular tools are applied in diagnosis of the infection and prediction of its effects. Serological assays are helpful in determination of immune status of birds. Hemagglutination inhibition (HI) is a serologic test that commonly used in diagnostic laboratories. This study was undertaken to demonstrate seroprevalence of H9N2 subtype in broiler chickens of Northwest of Iran. Materials and Methods: 310 blood samples collected from 25 broiler flocks in slaughterhouses of West Azarbayjan, Iran. Serum samples subjected to haemagglutination inhibition test. Statistical analysis was carried out using SPSS 16.0 where applicable. Results and discussion: 40.6% of serums were positive. Mean antibody titer of avian influenza virus differed significantly between geographical locations in this survey (P<0.05). High prevalence of avian influenza virus antibodies in serum of birds emphasize that avian influenza has an important role in respiratory complexes in broiler chickens of this region, and probably throughout Iran. Biosecurity measures, monitoring and surveillance programs, and to some degree vaccination are effective tools to prevent introduction of infection and its economic losses.

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