The polymerase chain reaction was used to detect genomic sequences of the positive-stranded RNA of bovine viral diarrhea virus (BVDV), a member of the family Togaviridae. Using a set of 20-bp primers located within the conserved 3' region of the BVDV genome, we were able to consistently amplify a 205-bp target sequence from BVDV cDNA. BVDV RNAs from cell culture-propagated BVDV reference strains, diverse unrelated cytopathic and noncytopathic field isolates, and clinical serum samples were transcribed to cDNA by using avian myeloblastosis virus reverse transcriptase and further specifically amplified by using the polymerase chain reaction assay. The amplification assay was sensitive enough to detect one molecule of cloned BVDV cDNA. Reconstitution experiments conducted by adding decreasing amounts of BVDV (NADL strain) to BVDV-free serum indicated that the threshold of sensitivity of the assay was less than or equal to 1 50% tissue culture infective dose. These results show that the polymerase chain reaction may be used for the rapid detection of diverse strains of BVDV in cell cultures, biological products, and clinical specimens from cattle.