Description: The applicability and reliability were investigated of antigen enzyme linked immunosorbent assay (Ag ELISA) and reverse transcription polymerase chain reaction (RT-PCR) for the diagnosis of bovine viral diarrhoea (BVD) in pooled serum samples of persistently infected cattle. In this study 968 serum samples were tested and persistent infection was confirmed by Ag ELISA in six animals by sampling twice at a four week interval. Positive samples were tested undiluted and diluted by Ag ELISA and RT-PCR. Sera were diluted (fifi vefold) and tested once again by both methods. All undiluted samples were tested positive by Ag ELISA, while the end point dilution was 1:5. When RT-PCR was used, samples were shown to be positive to 1:125, and in one sample in a dilution of 1:625. We can conclude that Ag ELISA can be useful in the diagnosis of BVD in a maximum five pooled serum samples from persistently infected animals. RT-PCR shows greater sensitivity and thus is more appropriate for screening purposes when pooling of samples is recommended