The effects of an inactivated strain of Aujeszky's disease vaccine in cattle were investigated. It has not been possible to use vaccines licensed for use in pigs successfully in cattle even though cattle develop neutralizing antibodies to these vaccines. The addition of zinc compounds to the vaccines resulted in protection in cattle. The basis for the use of zinc is discussed. A mutant based vaccine was effective following local administration, but was not when administered parenterally. Anti-prostaglandin was not effective either, despite its successful use in sheep when administered with BHV1. The vaccine presents a prospect for immunising dogs and cats, and the addition of zinc compounds to other drugs and inducers is discussed.