Background.The etiology of Henoch-Schönlein purpura (HSP) has been ascribed to a variety of infectious and noninfectious agents. Because we encountered a patient with HSP who had evidence ofBartonella henselaeinfection and a prior report of a patient with systemic cat-scratch disease presenting as leukoclastic vasculitis, we investigated the association ofB. henselaeinfection with HSP.Methods.We determined the antibody titers toB. henselaeon the sera of 18 patients with HSP and on 57 controls. All patients presented with the characteristic leukoclastic rash of HSP. About one-half of the patients had joint or abdominal symptoms, and four had hematuria at presentation. An indirect immunofluorescent assay was used to determine serum antibody titers toB. henselae.Sera that were reactive at a dilution of 1/64 were considered positive.Results.Eight of the 57 (14%) control sera and 12 of the 18 (67%) patient sera were positive forB. henselaeantibody (P< 0.0001).Conclusion.The results of this study indicate a significant association of antecedentB. henselaeinfection with HSP. The frequency of this association (67%) exceeds that of previously ascribed etiologic agents for this disease, such as the group AStreptococcus.