BACKGROUND The aim of this study was to evaluate the usefulness of colloidal gold probes widely used in histochemistry and electronic microscopy for the serologic diagnosis of syphilis. METHODS One hundred eighty-nine sera which had been submitted to the traditional fluorescent trigenemic absorption (FTA-ABS) test and had later been tested with the new colloidal gold probe method (IAT-ABS). RESULTS Out of a total of 103 positive samples by FTA-ABS all were positive when tested by gold immunoprobes (sensitivity 100%). Eighty-six samples which were negative by immunofluorescence were all negative by IAT-ABS (specificity 100%). CONCLUSIONS The new method of colloidal gold probes with the current microscopy is useful for confirming serologic diagnosis of syphilis.