The glycoprotein E (gE) locus in the genome of pseudorabies virus (PRV) was used as an insertion site for the expression of glycoprotein E1 of classical swine fever virus (CSFV). Transcription of E1 in the recombinants M401, M402 or M403 was regulated by the gD promoter of PRV, the immediate early gene promoter of human cytomegalovirus, or the gE promoter of PRV, respectively. Groups of four pigs were vaccinated once intramuscularly with 106 plaque forming units (p.f.u.) of the recombinant viruses and challenged intranasally with 100 50% lethal doses of virulent CSFV and with 105 p.f.u. of virulent PRV. All pigs vaccinated with M402 were fully protected against both classical swine fever and pseudorabies.