Three serotypes (A, B and C) were distinguished based on serological differences between isolates of red clover necrotic mosaic virus (RCNMV). Isolate TpM34, representative of serotype A, induced the formation of antibody only against homologous antigen. By contrast, isolate TpM48, representative of serotype B, induced the formation of 3 groups of antibody; the group of type-specific antibody was present in a higher titre than the other two antibody groups. Isolate 63/70, representing serotype C, also induced the production of type-specific antibody in a higher titre as compared with antibodies reacting with type A and B antigens. The distinct behaviour of the 3 serotypes was also manifested on immunoelectrophoresis in agarose gel. In anionic barbital buffer, serotypes A and C showed a higher mobility than representatives of serotype B, but in cationic environment serotype A showed a higher mobility than serotypes B and C.