The prevalence of antibodies to pestiviruses was investigated in 4931 sheep, in 377 flocks, in four federal states of Austria, by means of an indirect elisa that detected antibodies to Border disease virus (bdv) and bovine viral diarrhoea virus (bvdv). The mean flock prevalence was 62·9 per cent and the mean individual prevalence was 29·4 per cent. Comparative neutralisation studies on the elisa-positive samples with bvdv type 1 (bvdv-1), bvdv type 2 (bvdv-2) and bdv recorded 336 samples with higher titres (more than four times average) to bvdv-1, three samples with higher titres to bvdv-2 and 55 samples with higher titres to bdv. The other samples did not show clear differences in antibody titres against the strains of pestivirus tested because of cross-reactions. The seroprevalence of pestiviruses in sheep was significantly higher on farms with cattle. There were significant regional differences between the prevalences in flocks and individual sheep, the highest prevalences being in the region of Austria where communal alpine pasturing of sheep, goats and cattle is an important part of farming.