Clinical, virological, and morphological investigations were carried out on a total of 36 rabbits experimentally infected with five strains of the Aujeszky's disease virus. Those of the test animals that were infected with strain K did not die or died showing no clinical manifestations; those infected with strains K1. B, and TB showed nervous disturbances and died strongly scratching the site of injection. The animals infected with strain KB exhibited respiratory disturbances showing no death cases. Histopathologically, nonpurulent meningoencephalitis of the central nervous system was established in all animals. The rabbits infected with strain K (resistant to trypsin and temperature changes) and those infected with strain KB these lesions were more slightly expressed. The lungs of the affected animals showed interstitial intralobular phenomonia of a lympho-histiocytic type as a reactive necroses in the liver and spleen. In the case of K1, B, and TB infections no changes in the lungs and spleen were noticed, however, the liver was analogously affected. Results showed that those of those of the strains that were with lower virulence did not cause the clinical picture of scratching; such strains proved neurotropic and even strongly pheumotropic. It is concluded that the clinical and morphologic aspects observed in experimentally infected rabbits can be referred to in diagnosing the causative agent, differentiating strains that are slightly pathogenic from strains that are pathogenic.