1. Department of Chemical Pathology, Charing Cross Hospital, London
2. Department of Biochemical Endocrinology, Chelsea Hospital for Women, London
3. Reproductive Endocrinology Laboratory, Department of Obstetrics and Gynaecology, University of Edinburgh, Edinburgh
4. Steroid EQAS Unit, Tenovus Institute for Cancer Research, Cardiff
5. Department of Chemical Pathology, St Mary's Hospital Medical School, London, UK