Indirect fluorescent antibody assay (IFA) is the most reliable test for detecting antibody to Bartonella henselae in the diagnosis of cat scratch disease (CSD). Recently, an ELISA test has been proposed, but conflicting results are reported. We compared IgG-IFA and IgG-IgM ELISA methods in CSD patients and in healthy children. We also tested ELISA specificity in a large group of healthy controls and in children with lymphoma-associated lymphadenopathy and with pyogenic lymphadenitis. The ELISA procedure was positive in 69/78 patients with CSD (sensitivity 89.6%), in 5/100 healthy children (specificity 95%), in 2/51 patients with non-Hodgkin's lymphoma or pyogenic lymphadenitis (specificity 96%) and in 27/296 blood donors (specificity 91.6%). In 34 patients with CSD, ELISA IgM and IgG responses decreased significantly between time of diagnosis of the disease and recovery. We found significantly higher IgG-ELISA titres in cat-owners, whether blood donors or healthy children, than in non-cat-owners. The IgG-IFA test gave positive results in 69/78 patients with CSD (sensitivity 89.6%) and in 5/62 healthy controls (specificity 92.5%). The ELISA method is a cheap, sensitive method for determining antibody response to Bartonella henselae infection and is also important for evaluating the clinical course of the disease and the efficacy of antibiotic therapy. The high specificity of ELISA in patients with non-Hodgkin's lymphoma will help the clinician to exclude a potentially life-threatening disease associated with lymphadenopathy.