The objective of this study aimed at applying the oral juice (OJ) sampling method in comparison with tissue samples and use of PCR/RT-PCR techniques in identifying some pathogenous viruses causing respiratory disorders in pigs in several pig farms in Southern provinces from 2 kinds of these samples. Twelve sets of lung and internal organ specimens, and 32 OJ samples collected from 12 pig farms, which were having clinic signs of respiratory disorders in the post weaning pigs in Dong Nai province, Ho Chi Minh city and Ba Ria - Vung Tau province as the materials for this study. The initial results of study showed that OJ could be used to determine the prevalence of PRRSV and PCV2, which was mentioned similarly in some previous studies in foreign countries. The PCV2 detection rate in OJ samples was rather high, up to 81.3 percent, following by the PRRS virus (5.9 percent) and no CSFV was detected. The detection rate of CSFV, PRRSV from tissue samples was significant higher than that of OJ samples but the detection result of PCV2 was opposite. The highest detection rate of PCV2 from OJ samples was (over 80 percent) compared to 57.7 percent (of the PCV2 detection rate) from tissue samples. There were 72.7 percent of PRRSV detected from tissue samples and only 10.0 percent of PRRSV was detected from OJ samples. The detection rate of CSFV was lower in this survey, only 22.2 percent of CSFV from the tissue samples and 0 percent of CSFV from the OJ samples. There were 22.2 percent (2/9) farms infected with all of three viruses (PRRSV, CSFV and PCV2) and 55.6 percent (5/9) farms infected with both PRRSV and PCV2.