A reverse transcription-polymerase chain reaction (RTPCR) test was developed to differentiate between H1 and H3 subtypes of swine influenza virus (SIV). The sensitivity and specificity of this test was evaluated by comparing the results of the PCR test with subtyping results of an immunological assay performed at the National Veterinary Services Laboratories (NVSL). The test was performed on 68 eggderived SIV isolates, as well as directly on 30 lung homogenates. The data suggest that a PCR-based assay may be a reliable screening test for SIV both from egg fluid and directly from lung tissue
