Phylogenetic trees of the nucleotide sequences for the ORF2, ORF3, ORF4, ORF5, and NSP2 genes of the Chinese isolates (LS-4, HM-1, HQ-5, HQ-6, GC-2, GCH-3 and ST-7) and related reference viruses. The evolutionary relationships among these viruses were estimated by the neighbor-joining method with 100 bootstraps by using PHYLIP version 3.67. Alignments of each influenza virus sequence were generated using program Clustal W. The compared sequence regions were as follows: (771 bp) of ORF2, (777 bp) of ORF3; (552bp) of ORF4, (603 bp) of ORF5 and (893 bp) of NSP2. Black triangles indicate the virus isolates were isolated in this study. Two main subgroups of PRRSV isolates (I and II) are indicated for ORF2-5 and NSP2 genes.