A chimeric pestivirus of border disease virus Gifhorn and bovine viral diarrhea virus CP7 (Meyers et al., 1996) was constructed. Virulence, immunogenicity and vaccine properties of the chimeric virus were studied in a vaccination-challenge experiment in pigs. The chimeric virus proved to be avirulent and neither chimeric virus nor viral RNA was detected in serum after vaccination. The safety of the vaccine was tested by horizontal transmission to sentinel pigs, which remained uninfected. The vaccine efficacy was examined by challenge infection with classical swine fever virus (CSFV) Eystrup. In 'challenge controls', the viral load of CSFV coincided with the development of pronounced clinical symptoms. In contrast, the vaccinated pigs showed transient and weak clinical signs. Analysis of the viral load in these pigs showed 1000-fold lower viral RNA levels compared to 'challenge controls' and horizontal transmission of challenge virus to sentinel pigs was not observed.