The characteristics and the working modalities of ELISA (Enzyme Linked Immunosorbent Assay) are outlined at the onset. Subsequently, the Authors refer the data relevant to the use of ELISA in the syphilis serodiagnosis, by describing the operative phases for the working out of the test with the enzyme peroxidase, and reporting the results of the clinical investigation performed on primary and secondary syphilis in progress, on treated primary and secondary syphilis (examinations performed 1 to 10 years after the end of therapy), on healthy blood donors, and on samples of false biological positivities. On the basis of the analysis of the results, the Authors feel that ELISA for its characteristics of sensitivity, easiness in carrying out, rapidity and reproducibility, might find a rational indication in the modern serodiagnosis of the syphilis.