SummaryIsolates of parsnip yellow fleck virus (PYFV) from parsnip (P‐121), celery (CV506 and CV065) andHeracleum sphondylium(Hs2) were serologically close to each other but distant from isolates from carrot (Dc2 and Dc5) andAnthriscus sylvestris(A‐421 and As2), which were in turn close to each other serologically. The two groups of isolates also differed from each other in host range. Minor differences in immunological reactions and in host range and symptomatology were observed between isolates in each group. Particles of all eight isolates had similar RNA and protein compositions. The data confirm that PYFV isolates fall into two major serotypes, those from parsnip, celery andH. sphondyliumbelonging to the P‐121 serotype and those from carrot andA. sylvestrisbelonging to the A‐421 s