“…-Determination of plasma noradrenaline concentration [noradrenaline] is currently throught to be a useful index of Correspondence: Dr H. Ibsen, Department of Clinical Physiology, Glostrup Hospital, 2600 Glostrup, Denmark. sympathetic nerve activity (Christensen, 1979;Lake, Ziegler, Coleman & Kopin, 1977). Whereas some investigators have found increased plasma [noradrenalinel or increased urinary excretion rate for catecholamines (De Champlain, Farley, Cousineau & Van Ameringen, 1976;DeQuattro, Campese, Miura & Meijer, 1976;Esler, Julius, Zweifler, Randall, Harburg, Gardiner & DeQuatro, 1977) in a sizeable fraction of patients with essential hypertension, others have found completely normal values (Berglund,Tibblin & Aurell, 1975;Lake el al., 1977;Pedersen & Christensen, 1975).…”