Human rotavirus strain K8, which possesses unique VP4 neutralization epitopes, was examined by RNA-RNA hybridization to determine its genogroup. While it possessed four gene segments that formed hybrids with strain Wa (a prototype of the Wa genogroup), strain K8 possessed seven gene segments, including gene segment 4, that formed hybrids with strain AU-1 (a prototype of the AU-1 genogroup) which has been shown to share a unique gene 4 allele with feline rotaviruses. These results suggest that strain K8 is an intergenogroup reassortant formed in nature between a member of the Wa genogroup and a member of the AU-1 genogroup.