The genetic and antigenic characteristics of the Amur (AMR) and Far East (FE) virus lineages, which are both within the genus Hantavirus, were studied. Representative viruses, H5 and B78 for AMR and Bao 14 for FE, were used. The entire small (S) and medium (M) segments, except for the 3'- and 5'-ends, were sequenced. The deduced amino acid sequences of AMR had 96.7 and 92.0-92.2% identities with the Hantaan (HTN) virus in the S and M segments, respectively. The amino acid sequences of FE had 99.1 and 97.9% identities in the S and M segments, respectively. The three viral strains and HTN virus had similar binding patterns to a panel of monoclonal antibodies (MAbs), except that one MAb did not bind AMR. However, sera from Apodemus peninsulae, naturally infected with AMR virus, neutralized homologous viruses at 1:160 to 1:320 dilutions and HTN at 1:20 to 1:40 dilutions. The anti-AMR serum neutralized homologous viruses at a 1:80 dilution and HTN at a 1:40 dilution. The anti-HTN serum did not neutralize AMR (<1:40 dilution), although it had a high neutralizing titer (1:320) against the homologous virus. Therefore, we suggest that AMR virus may constitute a distinct serotype within the genus Hantavirus.