AbstractThis chapter focuses on the methods suited for routine testing of plant viruses and viroids, i.e. enzyme-based immunoassays (EIAs), and briefly discusses other serological detection techniques which build on the specific interaction between antibodies and the protein surface of disease agents. The principles and stepwise protocols for serological testing methods are described, and information on method optimization, variations, advantages and disadvantages are discussed. Further included are practical notes, interpretation of data, notes on pitfalls and trouble shooting.