Ecological and bacteriologic observations of small mammals captured in Dhaka, Bangladesh, indicated that Bartonella infections occurred in high prevalence among lesser bandicoot rats (Bandicota bengalensis), black rats (Rattus rattus), and house shrews (Suncus murinus). Sequence analysis of the citrate synthase gene of Bartonella isolates showed that small mammals in Bangladesh harbored a diverse assemblage of strains. Some cultures were genetically related to Bartonella elizabethae, a species identified from a human patient in the United States. Sequences of some other cultures from Bandicota and Rattus rats were identical to sequences of cultures from domestic rats in France, Portugal, and the United States. The finding of Bartonella species in a high proportion of the mammalian samples from Dhaka suggests the need to study whether these agents might be responsible for human cases of febrile illness of unknown etiology in Bangladesh and elsewhere in south Asia.