Objectives: Newcastle disease (ND) is a highly contagious infectious disease of poultry and many species of birds with huge economic losses. ND is a common problem in poultry farms of Iran. 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. Material and Methods: In order to determine NDV antibody status in broiler flocks of West and East Azarbayjan at the end of rearing period, 383 blood samples collected from 2 slaughterhouses in West Azarbayjan and subjected to HI test. Statistical analysis was carried out using SPSS version 16.0 where applicable. Results and discussion: Mean antibody titer for NDV was 5.31. 40.6% of samples were positive for NDV antibodies. Mean of HI titers differed significantly between geographical areas (P<0.05). High prevalence of NDV infections in poultry flocks indicates that NDV has an important role in respiratory complexes of poultry in this region and probably throughout Iran. Results of such surveys show that present applied strategies are not fully effective in the case of this infection. Biosecurity measures, vaccination programs and surveillance are altogether effective strategies in prevention of infection. Because of serology limitations, it is necessary to serological assays, virus isolation and molecular methods are applied altogether, to better evaluate NDV status in poultry flocks.

Keywords