Forty-six patients presenting with chronic orofacial muscle pain and eight age- and sex-matched control subjects were investigated for the carriage prevalence of, and exotoxin production by, coagulase-negative staphylococci (CNS). The eight control subjects were selected from an initial group of 41 subjects on the basis of the absence of musculoskeletal symptoms. There was a significantly higher prevalence and multiple carriage of four or more strains of CNS in patients with chronic muscle pain than in control subjects (23 versus 9 isolates/10 subjects). Two of the 103 CNS isolates from patients with muscle pain and none from the control subjects produced toxic shock syndrome toxin 1 (TSST-1), suggesting that pyrogenic toxins do not significantly contribute to the aetiology of chronic muscle pain. There was a significantly higher prevalence of delta-haemolysin (41 of 114) and 'horse'-haemolysin (56 of 114) production by CNS isolates from patients with chronic muscle pain compared with those from control subjects. None of the control subjects was colonised with CNS that produced significant amount of either delta- or 'horse'-haemolysin, whereas 35 of 44 patients with chronic orofacial muscle pain were colonised with CNS that produced significant amounts of 'horse'-haemolysin, 37 that produced delta-haemolysin and 33 that produced both delta- and horse-haemolysin. This study suggests that membrane-damaging toxins, like delta- and 'horse'-haemolysin, may play a role in the aetiology of chronic orofacial muscle pain.