Two new enzyme-linked immunosorbent assays (ELISA), one for the measurement of immunoglobulin G (IgG) (Captia Syphilis-G) and one for the measurement of IgM (Captia Syphilis-M), were evaluated for detecting antibodies to Treponema pallidum. Serum samples from 169 patients, 96 with various stages of untreated syphilis, 63 with treated syphilis, and 10 who were noninfected, were investigated. All sera were also examined by traditional treponemal and cardiolipin tests and by the fluorescent treponemal antibody absorption (FTA-ABS) test for 19S(IgM). The overall sensitivity of Captia Syphilis-G was 98.3%. The IgG ELISA was very sensitive (100%) in all stages of untreated syphilis, except in primary syphilis (82%). In all diagnostic groups of syphilis, the reactivity of Captia Syphilis-M was similar to that of the 19S(IgM) FTA-ABS test, except in reinfections, in which the IgM capture ELISA was less sensitive. False-positive IgM capture ELISA results were not found in the 10 neonates born to mothers adequately treated for syphilis. However, of six serum samples containing rheumatoid factor, two were reactive in the Captia Syphilis-M test but not in the 19S(IgM) FTA-ABS test. This indicated that the specificity of the IgM capture ELISA was not absolute. All serum samples from treated patients were reactive in the IgG ELISA, but only 15 samples were reactive in the IgM capture ELISA, which appeared to be as effective as the 19S(IgM) FTA-ABS test in monitoring the effect of treatment. Simultaneous measurement of IgG and IgM antibodies for T. pallidum by the Captia immunoassays appears to be an efficient and simple method for confirming the diagnosis of syphilis as well as for indicating whether active disease is present.