Two commercially available serologic tests for use in diagnosing Lyme borreliosis were evaluated by using a test panel comprised of sera from patients diagnosed with Lyme borreliosis, non-Lyme disease controls, and healthy subjects. The test methods examined were a Western blot assay and an immunodot assay. The study was initiated to determine how the immunodot assay, which contains purified and recombinant proteins to those borrelial antigens recommended for immunoglobulin M (IgM) detection in the Dearborn criteria, would compare with the Western blot assay as a confirmatory method for serologic diagnosis of Lyme borreliosis. Results obtained showed that the two test methods performed comparably for detecting IgG antibodies. For IgM antibody detection, the immunodot and Western blot assays had similar sensitivities; however, the immunodot assay was more specific and had greater positive predictive value than the Western blot assay. The results obtained indicate that the immunodot assay performs as well as or better than the Western blot assay for diagnosing Lyme borreliosis. Furthermore, because it uses a limited panel (n = 5) of antigens, the immunodot is easier to read and interpret than standard Western blots.