Cells infected with Pseudorabies virus (PrV) and fixed with formaldehyde were evaluated as a vaccine against Aujeszky's disease. Mice and pigs inoculated with fixed cells showed no clinical signs. In a challenge test, all fixed cells conferred protection on mice and pigs. Although pigs showed slight symptoms, they were restored to normal health within a few days. These results demonstrate that PrV-infected cells fixed with formaldehyde function as a vaccine against Aujeszky's disease and serve as a novel type of vaccine which is easy to make, and is both safe and effective.