We performed the present study to determine the rate of concordance of the fluorescent treponemal antibody absorption test (FTA-ABS) and of the microhemagglutination assay for antibodies to Treponema pallidum (MHA-TP) with the passive particle agglutination test (TP.PA) in patients with early syphilis and to observe the reactivity of the rapid plasma reagin (RPR), MHA-TP, and the TP.PA tests for 1 year after therapy. The study included 449 people who were given therapy if they had syphilis and followed up for 1 year. The rate of concordance of the TP.PA with the MHA-TP was 98.4%, and it was 98.9% with the FTA-ABS. During follow-up, a significant decrease of antibodies was found in 56%, 26%, and 70% of the patients when using the RPR, the MHA-TP, and the TP.PA, respectively. The TP.PA seems to be an adequate routine assay for the diagnosis of syphilis, being as sensitive as the FTA-ABS test in primary syphilis and as useful as the RPR test in monitoring therapy.