Claims have been made that certain diagnostic devices should be routinely used to differentiate between jaw dysfunction and normal variation and between various pathologic conditions of the temporomandibular joint. The claims that jaw-tracking devices have diagnostic value for detecting TMD are not well supported by the scientific evidence. The clinical usefulness of electromyography devices is limited because of technical, methodologic, and data interpretation problems, as well as significant overlap between asymptomatic and symptomatic groups. Claims for the use of sonography and vibratography machines to discriminate between various intracapsular TMJ conditions have not been substantiated by well-designed research. Until acceptable levels of technical and diagnostic validity have been clearly established, these diagnostic devices cannot be relied on as aids in differential diagnosis or in clinical decision making in the TMD field.