One hundred seven domestic cats from The Philippines were serologically tested to establish the prevalence of Bartonella infection. A subset of 31 of these cats also had whole blood collected to tentatively isolate Bartonella strains. Bartonella henselae and B. clarridgeiae were isolated from 19 (61%) of these cats. Bartonella henselae type I was isolated from 17 (89%) of the 19 culture-positive cats. Six cats (31%) were infected with B. clarridgeiae, of which four were coinfected with B. henselae. Sixty-eight percent (73 of 107) and 65% (70 of 107) of the cats had antibodies to B. henselae and B. clarridgeiae, respectively, detected by an immunofluorescence antibody (IFA) test at a titer > or = 1:64. When tested by enzyme immunoassay (EIA), 67 cats (62.6%) had antibodies to B. henselae and 71 cats (66.4%) had antibodies to B. clarridgeiae. Compared with the IFA test, the B. henselae EIA had a sensitivity of 90.4% and a specificity of 97%, with positive and negative predictive values of 98.5% and 82.5%, respectively. Similarly, the B. clarridgeiae EIA had a sensitivity of 97% and a specificity of 92% specificity, with positive and negative predictive values of 95.8% and 94.4%, respectively. The presence of antibodies to Bartonella was strongly associated with flea infestation. Domestic cats represent a large reservoir of Bartonella infection in the Philippines.