In the Netherlands the Central Veterinary Institute (CVI) and the Animal Health Services carried out investigations on aetiology, pathogenesis, therapy and prevention of Atrophic Rhinitis (AR) since 1970. Since the discovery of AR toxin in AR pathogenic P. multocida in SPF piglets, quicker and cheaper tests were developed e.g. the mouse test and guinea pig skin test. Today ELISA-tests with poly- and monoclonals are also available. The CVI carried out DNA probes and is developing a PCR-test. Tests to detect a natural infection were difficult to develop. The SN test by Bechmann, the skin test by Schimmelpfenning and the ELISA test by Foged give some perspectives. From investigations with B. bronchiseptica in piglets, it appears that the role of this germ is overestimated in the development of AR. On 16-week-old pigs an infection with AR toxigenic P. multocida caused conchae atrophy and septum deviation within 4 weeks. This fact has to be taken into account concerning the preventive medications in piglets. Only high maternal antibody titres against the AR toxin are able to protect the piglets for a sufficiently long period. Conchae atrophy and brachygnathia superior are indicators for suspicion of AR but do not prove the diagnosis of AR. By means of selective agars the isolation of P. multocida from nose, tonsils and lungs could be improved. The incubation period of clinical AR may last longer than two years. The AR pathogenic P. multocida is predominantly transmitted by pigs, incidentally also by rabbits, cattle, sheep, goat, poultry, dogs and cats. Humans can get infected and diseased. The AR pathogenic P. multocida has to be classified as a zoonosis. By way of stamping out and air filtering the transmission can be prevented. Vaccination cannot avoid an infection with the AR pathogenic P. multocida. The Animal Health Services developed a program to certify breeding herds 'free of AR pathogenic P. multocida'.