1. Department of Cardiology, St George's Hospital Medical School, Cranmer Terrace, London SW 17 ORE, U.K.
2. Division d'Hypertension, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland
3. Blood Pressure Unit, St George's Hospital Medical School, Cranmer Terrace, London SW 17 ORE, U.K.
4. Imperial College National Heart and Lung Institute Heart Science Centre, Harefield UB9 6JH, U.K.
5. Department of Chemical Pathology, St Helier Hospital, Carshalton, Surrey
6. Clinical Pharmacology Unit, Department of Pharmacology and Clinical Pharmacology, St George's Hospital Medical School, Cranmer Terrace, London SW 17 ORE, U.K.