The aim of this study was to investigate whether the treatment effect of intramuscular glucocorticoid injection differs between paitents with fibromyalgia and those with localized myalgia of the masseter mucle concerning pain, tenderness to digital palpation, pressure pain threshold, pressure pain tolderance level, maximum voluntary occlusal force, or intramuscular temperature. Twenty-five patients with fibromyalgia and 25 patients with localized myalgia of th e masseter muscle were first asked to assess their pain on a visual analogue scale; afterward, a routine clinical exmaination, including tenderness to digital palatpion, was performed. For each patient, the pressure pain threshold, pressure pain todlerance level, and maximum voluntary occlusal force, as well as the intramuscular temperature, were recorded. Finally each patient received an injection of glucocorticoid. The examination and glucocorticoid treatment were repeated after approximately 2 weeks, and a follow-up was perfored after another 5 weeks. In the fibromyalgia group, there was a reduced tenderness to digital palpation in response to the treatment. The localized myalgia group responded with a general improvement of symptoms as well as a significant reduction of pain intensity and tenderness to digital palpation. The results of this study indicate that patients with fibromyalgia and localized myalgia in many respects show a similar response to local glucocorticoid treatment.