EDITOR—Collinge et al recommend that tonsil biopsy be considered in all those in whom newvariant Creutzfeldt-Jakob disease is suspected.1 Though the detection of protease resistant prion protein in tonsillar tissue from a young person with a rapidly progressive dementia may have a high specificity for this diagnosis, there are no published data on sensitivity, specificity, or safety; the procedure carries the risk of haemorrhage and infection as well as the risks associated with anaesthesia. Some patients clinically suspected of havingnew variant Creutzfeldt-Jakob disease, and therefore potential candidates for tonsil biopsy, have subsequently recovered.2 Further information is obviously required, and we concur with the recommendation of a recent WHO consultation that …