AbstractAn irnmunogold-silver stainingmethod wasused to identifyTreponemapallidumspirochetes in formalin fixed tissue. In an indirect immunohistochemical procedure, the colloidal gold particles bound to the secondary antibody were visualized by a silver developing solution to create a brown-black reaction product. This brown-black staining is similar to the stain generated with a Warthin-Starry technique. This method was superior to such techniques as the avidin-biotin complex immunoperoxidase method and indirect immunofluorescence method with ammonium hydroxide treatment and could also beused to stain other spirochetes and antigens that are difficult to visualize with other immunohistochemical techniques. (The J Histotechnol14:243, 1991)