There are three basic categories of methods used in the diagnosis of virus infections: indirect examination, direct examination and serology. The virus in the clinical specimen is amplified by growing in tissue culture, embryonated chicken eggs or animals. The presence of growing virus is detected by the specific changes such as cytopathic effect, etc. In direct examination, the clinical specimen is examined directly for the presence of virus particles, virus antigens or virus nucleic acids. Direct, simple, sensitive and rapid methods, especially molecular methods are increasinly used. Serology is used to evaluate the course of an infection, or determine if it is a primary or a reinfection and if acute or chronic. Serologic diagnosis is used for viruses that are difficult to isolate and grow in cell culture and viruses with a slow course of disease (hepatitis viruses, HIV or EBV).