Viruses of the genus 'Norwalk-like viruses' (NLVs) detected in humans have been genetically classified into two major genetic groups, genogroups I and II (GI and GII), which together are made up of at least 14 genetic subgroups. However, a comparable classification of NLVs in other species remains to be carried out. We sequenced a 2-kb region from within the RNA polymerase gene to the 3' end of open reading frame 2 (ORF2) of two NLV strains previously detected in the caecum contents of healthy pigs. The sequences of the entire ORF2 of these two NLV strains were analyzed for their genetic relationships to 15 human strains, which have already been reported and used as references for the genetic classification of human NLV strains, and additional two strains; one, a human strain which has recently been reported and appears to represent a new genetic subgroup of GII; and the other, an animal NLV strain. Analysis of a matrix showing pairwise identities and topology of a neighbor-joining tree showed that the two swine strains could be classified into a new genetic subgroup of GII on the basis of the amino acid sequences of the entire capsid protein. Grouping of the two swine strains was well corroborated by results of similar analyses of nucleotide sequences of the entire ORF2 and of a 510 base region at the 3' end of ORF1.