Professor Esler developed a unique radiotracer method for the neurochemical study of the sympathetic nervous system in humans. Esler's noradrenaline "spillover" method allows quantification of sympathetic function over time and in comparisons between individuals, and has been widely adopted internationally, as illustrated by its use in the April 1998 studies of neural circulatory control on board Space Shuttle Columbia. The method has allowed Esler to show that enhanced sympathetic activity is probably the major mechanism initiating high blood pressure; regulation involves the CNS noradrenergic neurons, which determine the 'defence' pattern of sympathetic activity in response to longterm stress. The other major discovery has been in connection with heart failure, where results obtained were pivotal to the understanding of the neural pathophysiology of heart failure, providing the theoretical basis for the recent successful use of ß-adrenergic blockers in this condition.