Seven different epitopes on arabis mosaic virus (ArMV) were discerned. Neo-, crypto-, and epitopes exposed on the virion and isolated coat protein were differentiated by their reactivity with monoclonal antibodies in an indirect enzyme-linked immunosorbent assay. The monoclonal antibodies, produced in vitro and in vivo, were of IgGl, IgM and IgA isotype. No epitope exclusively specific for one isolate was found. One epitope was specific for ArMV isolates only. With the common epitopes an operational antigenic map was devised. An immunological relationship between nepoviruses of different serological subgroups was demonstrated. Grapevine fanleaf virus, a member of the ArMV subgroup could not be shown to expose crossreactive epitopes. For serotyping ArMV isolates were discriminated by comparing the reactivity of two or more monoclonal antibodies specific for different epitopes.