The literature on fibrositis (fibromyalgia), which originated in the early years of the last century in the UK and proliferated there in the first half of this century, has since diminished there in the last 30 years or so, but has increased in Canada and the US. Criteria suggested for diagnosis have created a syndrome with no diagnostic tests, serological or radiological signs, and no truly objective physical signs, but with predictable tender spots on pressure. The syndrome is largely, but not completely, confined to females, mostly of middle age; the symptoms include widespread aching of more than 3 months' duration, disturbed sleep, morning fatigue and stiffness, a failure to respond satisfactorily to any one form of therapy and a tendency to persist over long periods, but without permanent tissue changes. Features of psychological disturbance are present in many patients but not in all or even the majority. Definition of the condition as a disorder of pain modulation - a pain amplification syndrome - would seem to fit the facts best. Most would agree that an abnormal response to stress is an important factor in the appearance of the syndrome, as other stress related disorders, such as the irritable bowel syndrome and tension headaches, may coexist. Response to therapy, whether physical or pharmacological, is on the whole unsatisfactory. This type of patient has been well recognised in hospital clinic and general practice for many years.(ABSTRACT TRUNCATED AT 250 WORDS)