The study of 26 B. bronchiseptica strains with typical morphological and biochemical properties resulted in the detection of 8 strains having the main specific agglutinogens of 3 Bordetella species (serovars) in different combinations. The presence of the agglutinogens was confirmed in the agglutination test and the agglutinin adsorption test with the use of monospecific antisera to the main agglutinogens. The comparison of natural B. bronchiseptica serovars and artificial convertants (resulting from the conversion of B. parapertussis by B. pertussis phages) revealed their identical biochemical activity, their capacity for causing necrosis when injected intradermally into rabbits and for the formation of two types of colonies, differing in size and serological activity. In contrast to B. parapertussis convertants, B. bronchiseptica serovars had no lysogenic properties and were sensitive to B. pertussis and B. bronchiseptica phages.