We have previously used RT-PCR to amplify a 251 base pair fragment diagnostic for beet pseudo-yellows virus (BPYV) infection from several BPYV infected samples from Europe and the USA. This has now been shown by sequencing to represent a fragment of a heat shock protein (HSP)70 gene. Sequence analysis of the fragment revealed that it is closely similar to the C-terminal sequence of the HSP70 homologue gene of lettuce infectious yellows virus, a definitive closterovirus, and also has obvious sequence similarities to the HSP70 genes of the other previously sequenced closteroviruses citrus tristeza virus and beet yellows virus. This observation confirms that BPYV is an authentic closterovirus with a wide geographical distribution.