In reply: We thank the writers for their comments on the CFS guidelines1 and our joint letter about these guidelines.2

Hundertmark remarks on the interplay between physical and psychological factors in morbidity associated with CFS. We trust that our letter in no way contradicts this. Similarly, the inferences that Hickie drew from our letter are not supported by the text of the letter. Far from undermining the guidelines, our letter had the full support of the convenor of the working party responsible for the guidelines.

As clearly discussed in the guidelines, in the absence of specific diagnostic tests it is likely that a range of factors may contribute to the pathogenesis of CFS. Assumption of a primarily "psychological" pathogenesis is as unjustified as assumption of a primary "physical" basis. There are "abnormal" test results in many people with CFS, including abnormalities of the hypothalamic–pituitary–adrenal axis and some abnormalities of immune function. As stated, it is controversial whether such abnormalities are primary or secondary.

While cognitive–behavioural therapy with graded exercise is effective in some patients, the guidelines outline the deficiencies of the evidence which "significantly limit the generalisability of the findings". As the guidelines indicate, and as is supported by our letter, treatment should be designed in partnership with the patient, and tailored according to the patient's capacity and response.

Finally, as implied by Beard's letter, we restate the need for further research into the aetiology, pathology and treatment of CFS.

We believe that effective progress in the management of this complex and mysterious illness will be best achieved by positive and cooperative rather than adversarial relationships between those suffering from the condition and the doctors and researchers attempting to help them.