Disclosed are antibodies that bind to the antigenic proteins GroES, RpIL, GroEL, SodB, UbiG, the ABC transporter, and an expressed antigenic protein of unknown function (the "BepA" protein) of Bartonella henselae, and use of these antigenic proteins in immunoassays in order to determine whether a sample from a subject contains one or more of these antibodies. Presence of such an antibody in the subject indicates that the subject is or was infected with Bartonella henselae, or indicates that the subject has an increased likelihood of being infected presently or in the past with Bartonella henselae. Also disclosed are kits for performing immunoassays, wherein each kit contains one or more of these antigenic proteins and also contains the reagents necessary for conducting an immunoassay.