Four 60-day-old pigs were experimentally infected with Bordetella bronchiseptica at a state in which the animals were clinicylly normal. A single pig only, killed on the 180th day, presented a slight deflection of septum nasi. Morphologically, there were severe dystrophic and necrotic changes in the mucosa of the conchae, the nasal cartilages as well as in the bones. The pathogen was reisolated from two of the pigs. Clinical and morphological investigations were carried out also with spontaneously affected animals, isolating Pasteurella multocida, Pseudomonas aeruginosa, and Mycoplasma organisms, but not Bordetella bronchiseptic. Morphologically, there were in 37 of the pigs severe dystrophic and necrotic lesions in the nasal mucosa, cartilages, and bones. Basophilic inclusion bodies were demonstrated in the epithelial cells of the tubulous glands. It is concluded that a combined method of prophylaxis and treatment would be most effective, and of the drugs borgal has proved likewise most promising.