Northern blot analyses of RNAs from an Iranian strain of Peanut stunt virus (PSV-I Cucumovirus) using cloned cDNA probes to the genomic RNAs from two PSV strains, PSV-ER (subgroup I) and PSV-W (subgroup II), indicated that PSV-I RNA-3 is derived from a subgroup II strain. No hybridization signals, however, were detected with PSV-I RNAs 1 and 2 suggesting they are distinct from both subgroups I and II. Nucleotide (nt) sequence analysis of cloned cDNA fragments (1-1.5 kbp in size) representing PSV-I RNAs 1 and 2 showed that PSV-I is more closely related to subgroup II strains than to any other sequenced cucumovirus. The percent nt identity between RNA-1 sequences from PSV-I and PSV-ER or between PSV-I and PSV-W were 79.1% and 88.8%, respectively. The corresponding values for RNA-2 were 77.5% and 86.7%. Sequence comparison analyses of deduced amino acid sequence of cloned partial sequences of PSV-I RNAs 1 and 2 indicated that PSV-I 1a and 2a proteins are most closely related to those of subgroup II strains (93% identity). PSV-I supported the replication and encapsidation of PSV G-satellite RNA (G-satRNA), but not cucumber mosaic virus WL1-satRNA. PSV-I may be perceived as an Old World derivative of subgroup II strains, or it may represent a natural reassortment between a subgroup II (RNA-3) and an as yet uncharacterized subgroup of PSV strains (RNAs 1 and 2).