Just read Firestormm's post on Jennie's blog, and noticed an interesting point that I hadn't picked up on before: "What of other diseases for whom patients report similar feelings of a general ‘worsening’ of symptoms post-exertion? Does the above serve to make PEM unique to ME? Does it even have to?" Dr Snell only compared CFS patients to healthy controls, and did not compare against any other diseases. (Perhaps the significance of this is obvious, but I can be a bit slow on the uptake sometimes!) So we don't actually know if the results are unique to CFS patients. The tests might be able to distinguish CFS patients from healthy people, but may not necessarily distinguish CFS from other illnesses. More research needed, as always!