Bartonella henselae, an emerging pathogen bacterium, is the main causative agent of the cat scratch disease. While the first clinical descriptions were associated with immunosupressed patients, it is now more frequently observed in patients with normal immune status (endocarditis and bacteremia). Cats were found to be the only known reservoir of B. henselae. In this paper, we report the results obtained in the first study made to investigate the prevalence of B. henselae bacteremia and antibodies in domestic cats in Catalonia, Spain. Serum samples from 115 cats were tested for antibodies to B. henselae by immunofluorescent antibody testing, and 29.6% had a titer >or= 1:64. Seven B. henselae strains were isolated using standard culture techniques and amplification by a polymerase chain reaction and subsequent sequencing was performed on the intergenic spacer region between the 16 and 23S ribosomal RNA genes. Of all factors concerning the studied bacteremia rate (age, sex, habitat, presence of antibodies, contact with animals, parasites), only the presence of antibodies to B. henselae was statistically significant.