The toxigenic properties of Bordetella bronchiseptica strains associated with clinical atrophic rhinitis were compared using three biological assays: the guinea pig skin test, the mouse spleen atrophy and the suckling mice mortality assay. Forty one sick pigs were cultured and, in 20 of them B. bronchiseptica strains were isolated. Eighteen of the strains were toxigenic by at least one test. However, positivity did not always coincide amongst assays. This discrepancy raises the possibility of either differences in sensitivity between assays or the existence of more than one toxin.