The nucleotide sequence of the genomic RNA of Acyrthosiphon pisum virus was determined. The APV genome is 10,016 nucleotides in length, excluding the 3'-end poly(A) track, and contains two large open reading frames (ORFs), encoding proteins of 296,340 and 63,279 Da. The ORF1 is preceded by an untranslated leader sequence of 267 nucleotides. The ORF1 product contains sequence motifs characteristic of RNA-dependent RNA polymerases, chymotrypsin-like proteases, and helicases. Interviral sequence comparison revealed significant similarities with viruses belonging to the so-called picornavirus superfamily. The ORF2 is most likely expressed by a -1 translational frameshift and is followed by an untranslated sequence of 222 nucleotides. Internal amino acid sequences of three capsid proteins (66K, 34K, 23/24K) were determined. Comparison of the obtained amino acid sequences with the APV sequence disclosed that the structural proteins are located in the 3'-terminal half of the genome. The 34K protein is encoded by the ORF1, while the 66K protein contains both ORF1-(34K) and ORF2-derived sequences and is probably expressed by a translational frameshift. The 23/24K proteins most likely arise by proteolytic breakdown of the 34K protein. Although the deduced APV genomic organization in some aspects resembles that of the picornaviruses, its overall genomic organization indicates that APV is a distinct species only distantly related to the Picornaviridae.