|Abstract||Seven species-specific monoclonal antibodies (MAbs) to Bartonella quintana were produced and characterized. The MAbs were of the immunoglobulin G class and reacted only with 13 B. quintana strains in indirect microimmunofluorescence and Western immunoblotting assays. They did not react with eight other Bartonella spp., including Bartonella henselae, the most closely related species, and a selected MAb did also not react with nine other strains of gram-negative bacteria. The MAbs reacted mainly with a 34-kDa protein epitope of B. quintana which was shown to be species specific by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Four of five body lice experimentally infected with B. quintana were found to be positive for the organism in microimmunofluorescence assays with one MAb. These MAbs may provide a specific, simple, rapid, and low-cost tool for the identification of B. quintana and the diagnosis of infections due to the microorganism.