Newly developed vaccines in veterinary medicine can be classified into two categories. The first category comprises inactivated vaccines produced by "classical" methods such as inactivation of the virus by formalin and the use of A1(OH)3 as adjuvant. Besides, this category also includes live vaccines from attenuated virus. Thus, all of these vaccines represent no genuinely new developments and owe their origin to the fact that the importance of several virus diseases of animals has grown in the last years, making neccessary the rapid production of corresponding vaccines. Such virus diseases are infectious bovine rhinotracheitis/vulvovaginitis, enzootic rhinopneumonitis of cattle, virus diarrhoe of calves, rhinopneumonitis of horses, kennel cough of dogs and Marek's disease of chickens. The second category comprises inactivated vaccines which represent genuinely new developments through the use of more efficient chemicals for virus inactivation (ethylenimines) and more efficient adjuvants (oil emulsions, DEAE dextran). Such vaccines were especially developed with regard to foot-and-mouth disease and Aujeszky disease in pigs, where "classical" vaccines are rather inefficient. These types of vaccines are, however, also efficient in other animal species and with other viruses. Entirely new vaccines which are more or less still in an experimental stage are vaccines made from split products of viruses e.g. from glycoproteids of rabies virus, or made from membrane constituents of cells infected with avian herpes viruses.