According to the nucleotide sequences of classical swine fever virus(CSFV)and porcine reproductive and respiratory syndrome virus(PRRSV)in GenBank,two pairs of primers were designed and synthesized.A double RT-PCR was developed based on these two pairs of primers which amplified the CSFV virus-specific segment with 508bp and the PRRSV virus-specific segment with 432bp in sizes after the conditions of PCR were optimized.The results indicate that the double RT-PCR reaction after optimization show a good sensi...