multiple technological levels the necessity of developing vaccine quality control systems is one of the requirements of our  country Coordinated tests of the absence of externous agents in biological substances are considered as a major international concern for veterinary vaccines. Exogenous agents such as Newcastle disease virus, avian leukosis virus, infectious laryngotracheitis virus (ILTV), infectious bursal disease virus, infectious bronchitis virus, chicken anemia virus, hemorrhagic enteritis virus and reticuloendothelial virus. Identification methods for these external viral agents include: Serological testing of virus specific antibodies in vaccinated birds, virus isolation in vaccinated birds, virus isolation in embryonic eggs or cell cultures. Here's an overview of these methods.