Species of the genus Bartonella are currently recognized in growing numbers and are involved in an increasing variety of human diseases, mainly trench fever, Carrion's disease, bacillary angiomatosis, endocarditis, cat scratch dease, neuroretinities, and asymptomatic bacteremia. Amplification-based techniques enable detection and identification of the bacteria to be performed directly from clinical specimens. Partial ITS amplification and sequencing offers a sensitive means of intraspecies differentiation. Each Bartonella possesses a single, species-specific ITS. ribC is highly conserved at the species level. Primer oligonucleotides designed on the basis of localized differences with the ribC DNA region are used in species-specific assays for the differentiation of B. henselae and B. quintana, the two most commonly isolated Bartonella species. The PCR assay increases the diagnostic potential to detect and differentiate Bartonella species.