SummaryPlants with symptoms of barley yellow dwarf virus (BYDV) obtained in infection feeding assays of aphids collected in the field in Idaho between 1986 and 1988 were tested for virus transmissibility by possible aphid vectors. Isolates obtained during 1987–1988 were also tested with a range of polyclonal antisera which distinguished PAV, MAV, SGV, RPV and RMV serotypes. In 1989 some Idaho (ID) BYDV isolates, maintained as standards for comparison, were serotyped and tested for aphid transmissibility, using 11 species of aphids.There was not always the expected correspondence between serotype and vector specificity for ID isolates. For isolates obtained from field‐collectedRhopalosiphum padi, vector transmissibility and serotype corresponded with previous reports; however, 44% of isolates which were serotyped as RMV were also transmissible by species other thanRhopalosiphum maidis.Similarly, the transmissibility of the ID laboratory standards did not always conform to the reported vector specificity of serotypes. The laboratory ID‐MAV culture was transmitted byMetopolophium dirhodumandMyzus persicaeas well as bySitobion avenae.The laboratory ID‐SGV culture was transmitted byR. padiand 5.avenaeas well as bySchizaphis graminum.The ID‐RPV culture was transmitted byS. graminumandRhopalosiphum insertumas well asR. padi.Both of two laboratory ID‐RMV cultures were transmissible byR. insertumandR. paditransmitted one of them. The results indicate that, for isolates collected in Idaho, vector specificity cannot be assumed from thei