Among the species that compose the expanding genus Bartonella, thus far only B. henselae and B. quintana have reportedly been isolated from humans in Europe. To evaluate the prevalence of Bartonella infection in Sweden, we conducted a retrospective serological examination of 126 human serum samples. These samples were analyzed for antibodies to B. henselae, B. quintana, and B. elizabethae. Serum samples from 100 blood donors, who spanned the ages of 20 to 60 and had no apparent clinical signs of illness, were also studied as a control group. An immunoglobulin G indirect fluorescence antibody assay revealed 4 and 8.3% Bartonella positivity rates for the blood donor and patient group, respectively, when a cutoff titer of 64 was chosen. Among the blood donors, four were seropositive to B. elizabethae; one of these also had concordant positive titer to B. henselae. In the patient group, 14 serum samples were positive against Bartonella spp. These serum specimens represented nine patients. In three of these seropositive patients, paired serum samples displayed a fourfold increase in antibody titer to at least one of the three antigens. These three patients are discussed. In this report we also present a case study of a 60-year-old Swedish male with fatal myocarditis. Postmortem serological analysis revealed a high titer against B. elizabethae. PCR and nucleotide sequencing of the myocardial tissue from this patient, and of liver tissue from one of the other three patients, showed sequences similar to B. quintana. The age, geographical origin, animal contacts, and serological response pattern to the different Bartonella antigens differed among the four patients. This study substantiates the presence of Bartonella spp. in Sweden, documents the seroreactivity to three Bartonella antigens in Swedish patients, and reports the first two cases of B. quintana-like infections in Sweden.