Native Electrophoresis and Western Blot Analysis (NEWeB) has been developed for the study of plant virus characteristics, among others, virus particle-protein interactions, electrophorotype formation, and strain separation. The method is based on the property of electrophoretic mobility of virus particles (VP) and proteins and combines the analytical capacity of electrophoresis with the specificity of western blot. One of its advantages is that it deals with entire VP that can be studied in cause and effect or in time-interval experiments. Some of the most interesting approaches include VP structural studies, VP interaction with host or viral proteins, and also the characterization of VP-protein complexes. In this protocol, NEWeB is used to demonstrate the interaction of Plum pox virus particles with the helper component, a virus encoded protein. It is expected that the method could be used in analogous studies of other viruses or large protein complexes, where similar principles apply.