The nucleotide sequence of a 1355 bp cDNA representing the 3'-terminal sequences of pea seed-borne mosaic virus (PSbMV) was determined. This sequence contained a single long open reading frame (ORF) of 1189 bp ending with a single TAA termination codon. Downstream from the ORF was an untranslatable region of 189 bp followed by eight bp of polyadenylate. The probable location of the PSbMV coat protein codons within the long ORF was determined by comparing the inferred amino acid sequence with other potyviral coat protein sequences and by examining the sequence for a potyviral polyprotein cleavage cassette sequence. Direct chemical sequencing of the PSbMV coat protein revealed it to be blocked at its amino terminus. A partial amino acid sequence representing the N terminus of the protease-resistant core of the coat protein was determined, however. Alignment of the PSbMV coat protein sequence and the sequences of seven other potyviral coat proteins revealed significant homology, ranging from 53.7% for potato virus Y strain D to 43.2% for tobacco vein mottling virus.