Part of genomic segment A of five recent European 'very virulent' (VV) isolates of infectious bursal disease virus, encoding the major, conformational, protective epitope, have been reverse-transcribed, amplified and cloned. Sequence analysis of 582 bases of VP2 showed that the four U.K. isolates are closely related to each other, differing by no more than two bases, but are distinct from the 'classical' type 1 strains (differing by at least 29 bases, or four amino acids, from any other strain and by 15 bases, or three amino acids, from the consensus sequence of all other strains). The U.K. isolates differ from an earlier VV isolate from the Netherlands by no more than five bases or two amino acids. The U.K. isolates differ by only one or two bases, with no amino acid changes, from the recently published sequence of a Japanese VV isolate.