“…The increased heart rate in borderline hypertensive subjects (Frohlich, Kozul, Tarazi & Dustan, 1970;Berglund, Wilhelmsen & Werko, 1974) and in established hypertension (Isacsson, 1972) has been taken as indirect evidence of increased sympathetic activity, as has also the increased cardiac output in hypertensive patients without organ damage (Sannerstedt, 1969). Haemodynamic studies, however, have shown the hyperkinetic circulation in labile as well as in established hypertension to be caused by a combination of increased sympathetic activity and decreased parasympathetic tone (Julius, Pascual & London, 1971 ;Korner, Shaw, Uther, West, McRitchie & Richards, 1973). Direct quantification of sympathetic nervous system activity by insertion of needle electrodes into efferent sympathetic nerves has not shown any increase (G. Wallin, W. Delius & K. E. Hagbarth, unpublished work).…”