Periodontal probing attachment level measurements and intraoral radiographs are used to assess the level of the clinical attachment and bone support in the diagnosis of periodontitis. Together these physical measurements of tooth support comprise the standard against which new diagnostic tests are compared. Since probing and radiographs provide a measure of the severity of attachment or bone loss at one point in time, serial measurements must be compared to determine whether periodontitis is progressive. Periodontal probing may be performed manually or by using controlled force electronic instruments. The resolution, depending on the instrument, will vary from 1.0 mm to 0.1 mm. Variations in probing force, size and shape of tip, location of tip placement, detection or reference landmarks for attachment level probing, degree of gingival inflammation, and transcription may adversely influence accuracy. Electronic probes offer the advantage of improved resolution, force control, and automatic recording, but the literature is inconsistent about the advantages in terms of repeatability and accuracy. Radiographic assessment of alveolar bone loss may be achieved by visual interpretation, measurement, or digital image analysis. While visual interpretation of unstandardized radiographs is insensitive to changes in bone, standardized radiographs can permit measurement of changes on the order of 0.2 mm when computerized methods are used. Newer techniques such as digital subtraction radiography permit detection of bony changes too small to be seen by the unaided eye and are over 95% sensitive and specific in detecting bony changes less than 10 mg.