As indicated by their nucleotide sequences bovine viral diarrhea viruses (BVD-virus) are genetically quite heterogenous. Despite differences in the nucleotide sequence in the NS3 region, we found that the derived amino acid sequence of all viral strains analyzed was identical and differed from that of classical swine fever viruses, thus allowing differentiation between bovine and porcine pestiviruses. Remarkably, the BVD viral strains were isolated over a time period of some 40 years in Europe, North America and New Zealand. The nucleotide sequence of the 5' untranslated genome region of a BVD virus recently isolated in Switzerland from a calf with hemorrhagic syndrome differs from that of BVD viruses causing similar symptoms in a large epidemic outbreak in North America.