1. Haematology Division, National Institute for Biological Standards and Control, Potters Bar, Herts.,
2. Division of Transfusion Medicine, University of Cambridge/National Blood Service, East Anglia Centre, Cambridge,
3. Department of Biochemistry, University of Limburg, Maastricht, The Netherlands,
4. Vascular Cell Biology Laboratory, Department of Chemical Pathology, Royal Free Hospital School of Medicine, London