Dark-field is a wet-preparation method for direct visualization of living T. pallidum spirochetes in material from syphilitic lesions. A microscope with a special dark-field condensor is required. This condensor prevents light from passing directly through the slide being viewed into the microscope viewing lenses but instead forces the light to pass to the periphery of the slide. Objects on the slide reflect some light up into the viewing lenses, so the objects appear white on a dark background. Dark-field was the only way to make the laboratory diagnosis of syphilis before serologic tests were available. The usual indications for this test are suspected primary stage syphilitic lesions and any suitable secondary stage lesion. Dark-field examination may be the only way to make a diagnosis early in the primary stage, since immunologic test antibodies often do not appear until late in the primary stage. Obtaining the specimen without contamination by blood or surface bacteria is very important. The lesion should be cleansed thoroughly with water or 0.85% saline and a sterile gauze pad. No soap or antiseptics should be used. Care must be taken not to produce bleeding, since red blood cells (RBCs) will obscure the organisms. After the lesion is blotted dry, a clear serous exudate should accumulate in a few minutes. If it does not, the lesion may be abraded gently with gauze, but not enough to cause bleeding. The serous fluid exudate is drawn off in a pipette or capillary tube for examination with a dark-field microscope. The causative organism, T. pallidum, has a characteristic morphology and motility on dark-field examination, but experience is necessary for interpretation, since nonpathogenic varieties of spirochetes may be found normally in the genital areas. Sensitivity with reasonable experience is reported to be about 75%. Dark-field examination by experienced personnel is no longer widely available in many areas because it is rarely ordered. If it is unavailable, a serologic test using the fluorescent treponemal antibody-absorbed (FTA-ABS) method could be substituted. However, the FTA-ABS test will miss 10%-20% of cases, with the possibility of error being greatest in the first week of the primary stage.