I have received about a dozen replies to my questionnare regarding sensitivity and accuracy. The diversity of answers to the two simple questions posed is very revealing, and indicative of the urgent need for clarification of certain basic concepts in clinical chemistry. I'd like to thank those who have replied, to whom I shall be sending comments (individually) very shortly. Meanwhile, it would be helpful if others would take the trouble to answer the questions, since it would be useful to have a broader overview of people's views should I - as I now intend - bring up this issue with the relevant European and international bodies. It should take no more than 2 minutes to answer the questions and e-post a reply. (Note that the names of repliers will remain confidential.) Roger Ekins Molecular Endocrinology UCL Medical School %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%