This monograph assesses the symptoms of jaw muscle pain and alterations in biochemistry and carriage of staphylococci. Three different study populations were assessed, two of which were blinded to the author. The studies clearly establish an association between toxicogenic staphylococci and jaw muscle pain in both sexes. These associations were homogeneous and were found whether the patients were selected on the basis of having jaw muscle pain or from within a population having another pain syndrome (ME/CFS). The studies associated the changes with variations in biochemistry and symptom expression within the jaw muscle pain patients. The biochemical alterations included deregulation of immune cell counts, cytokines, electrolyte and protein metabolism, and were associated with pain severity and illness duration and staphylococcal toxin production. From the data a model was developed which shows the mechanisms involved in the development of chronic pain in the jaw muscles.