The effects of iontophoretically applied dexamethasone in a lidocaine vehicle were compared with those of saline placebo in 53 patients with one of three diagnoses of painful temporomandibular joint pathologic conditions: disk displacement with reduction, disk displacement without reduction, and osteoarthritis. Both dexamethasone and the saline placebo produced a significant reduction in pain scores from baseline levels after the first two of three treatments. There were no observed differences, however, in pain report or mandibular range of motion between the dexamethasone and placebo groups. A trend for pain relief was noted in the subgroup that received dexamethasone with a diagnosis of osteoarthritis. Results may reflect varying degrees of inflammation or central nervous system hyperexcitability, or both, in this heterogeneous study sample. Potential confounding variables were lack of knowledge of actual drug penetration, the effects of electric current transmitted by the iontophoresor, and pain reduction caused by cyclic fluctuations in symptoms. These data suggest that iontophoretically applied dexamethasone is no more effective than saline placebo in providing pain relief in patients with temporomandibular joint pain.