Bordetella have been frequently detectable from lesioned lung material of swine as well as from the upper respiratory tracts of clinically intact animals. Pneumonia, different in extent, was produced in primarily specific pathogen free pigs by intratracheal and intranasal application of eight Bordetella isolates. Moderate to medium manifestations of focal pneumonia with scattered speckles developed, with severity depending on dosage and mode of infection. Histologically, they were characterised by vascular lesions and fibroblastic proliferation. This type of pneumonia thus was differentiated by the above characteristics from pneumonia caused by heamophils and Pasteurellae. Under conditions of natural exposure, Bordetella pneumonia can be expected to develop primarily due to defective host-patasite relationship. Bordetellae, in this context, are considered only conditionally pathogenic. Bordetellal infection will have to be taken into consideration in differential diagnosis whenever checks are made on pigs in industrialised units.