Three hybridomas (P1P3, D7 and 60.5) producing monoclonal antibodies (mAbs) against Bordetella pertussis lipopolysaccharide (LPS) were established. All reacted with the LPS from a typical, vaccine strain of B. pertussis (1414), but not with that of a variant strain (A100). Two of these mAbs (P1P3 and 60.5) cross-reacted with a B. bronchiseptica LPS; only one (P1P3) reacted with a B. parapertussis LPS. ELISA reactivities with intact LPSs, and defined partial structures covalently linked to bovine serum albumin, were compared. mAb 60.5 bound to the terminal region of a distal trisaccharide consisting of N-acetylated amino sugars. D7 reacted with a substructure which can be modified in the B. parapertussis and B. bronchiseptica LPSs by addition of a polymeric O-chain. P1P3 bound to a nonacetylated glucosamine substituted with L-glycero-D-manno-heptose, present in the 'core' of the B. pertussis LPS. These mAbs may be useful for rapid typing of Bordetella in clinical isolates.