1. From the Medical Research Council Blood Pressure Unit (S.B.H., R.F., G.C.I., A.F.L.) and the Biochemistry Department (M.H.D.), Western Infirmary, Glasgow; the Department of Pathological Biochemistry (G.H.B.), Royal Infirmary, Glasgow; Mount Vernon Hospital (C.J.W.F.), Northwood, Middlesex; and the Department of General Practice (G.C.M.W.), University of Glasgow, UK.