Bordetella pertussis cells express multiple virulence-associated surface proteins, including adenylate cyclase, agglutinogens 2 and 3, filamentous hemagglutinin, pertussis toxin, and outer-membrane protein (Omp) 30/32 and Omp91. Surface proteins that are not virulence-associated include three peptidoglycan-associated Omps of apparent molecular weights 40,000, 25,000, and 18,000. Omp40 is an anion-selective porin and is the most abundant surface protein of virulent and avirulent cells. Three independent approaches--immunomicroscopy, surface radioiodination, and isolation of Triton X-100-insoluble envelope proteins--suggest that the Triton-insoluble fraction of the B. pertussis cell envelope is the outer membrane. Agglutinogens 2 and 3 and filamentous hemagglutinin lie outside the outer membrane, the first two as fimbriae and the last as a microcapsule. Adenylate cyclase and pertussis toxin are present in the outer membrane but may be present transiently or present in small amounts.