Three different enzyme-linked immunosorbent assays (ELISA) and Western blot were compared in regard to the detection of antibodies to Borrelia burgdorferi in sera from 100 patients with erythema migrans and from 100 controls. For IgG detection, a commercial indirect ELISA kit with flagellum antigen (flagellum ELISA) was significantly more sensitive than the routinely-used indirect ELISA with sonicated whole-cell antigen (sonicate ELISA) (p = 0.008). The difference in positivity in the IgM test was of borderline significance (p = 0.058). An IgM antibody-capture ELISA with sonicated whole-cell antigen (capture ELISA) was significantly more sensitive than either the IgM sonicate ELISA (p less than 0.001) or IgM flagellum ELISA (p less than 0.001). With the Western blot pattern chosen as the criterion for positivity, IgM Western blot was at least equal to IgM capture ELISA in terms of the number of positive erythema migrans sera, but a frequent discrepancy between these two tests was noted as to positivity in individual sera. IgG Western blot was considered to be of less value for the diagnosis of current disease due to a high occurrence of positivity among controls.