Biological activities of lipopolysaccharides (LPS) extracted from Bordetella pertussis, B. parapertussis and B. bronchiseptica were compared with those of Escherichia coli LPS. The LPS preparations from B. pertussis showed biological activities comparable to those of E. coli LPS in terms of lethal toxicity in galactosamine-sensitized mice, pyrogenicity in rabbits, mitogenicity in C3H/He spleen cell cultures, macrophage activation, and induction of tumour necrosis factor. All the activities of LPS preparations from B. parapertussis, except mitogenicity, were lower than those of E. coli LPS. LPS from B. parapertussis gave the greatest mitogenic action of all those tested. Biological activities stronger than or comparable to those of E. coli LPS were observed for LPS from B. bronchiseptica.