On the basis of serological properties and host plant reactions pepper mottle virus (PepMoV) has been classified as a potyvirus related to, but distinct from, other pepper-infecting potyviruses, potato virus Y (PVY) and tobacco etch virus (TEV). Recent amino acid and nucleotide sequence data show that PepMoV is more closely related to PVY than previously assumed. PepMoV shows a high degree of homology to various PVY strains in both the coat protein and the 3' non-translated sequences, while unrelated potyviruses are generally less homologous in these regions. Detailed coat-protein amino acid sequence and 3' non-translated region (3' NTR) nucleotide sequence comparisons described in this paper confirm the close relationship between PepMoV and PVY and it is concluded that the isolate sequenced indeed represents a strain of PVY. Sequence data for several strains of PVY gave two groups with closer relationships among strains in a group than between groups.