Sera from 408 patients with untreated or treated syphilis were examined by three different tests to demonstrate treponema-specific 19S(IgM) antibodies. Antibody titers in the 19S(IgM)-fluorescent treponemal antibody (FTA) test and the solid phase haemadsorption assay (SPHA) did not correlate. The 19S(IGM)-Treponema pallidum haemagglutination assay (TPHA) and the SPHA partly correlated based on the concentration of treponema-specific 19S(IgM) antibodies in the patient's serum. Under experimental conditions antibody titres in the 19S(IGM)-FTA test and the 19S(IgM)-TPHA correlated consistently. For specificity and sensitivity, the 19S(IgM)-FTA test correlated best with the clinical findings in both untreated and successfully treated patients. Although the 19S(IgM)-TPHA has about the same degree of specificity, the reading of the results is technically more complicated. The specificity of the SPHA was very high. In patients with untreated syphilis, however, the SPHA is adversely affected by a high rate of false non-reactive results, since it consists of two reactions with appreciable differences in sensitivity. Thus, higher sensitivity cannot be expected in the SPHA. An immunoadsorption technique using an adequate antigen and a specific, enzyme-labelled antiserum might provide an alternative test which is simple to perform, highly specific, and consistently sensitive.