The relationship was studied between brain catecholamine systems, open-field behaviour and the development of hypertension in spontaneously hypertensive rats (SHR). Both the rise in blood pressure and the increased open-field rearing activity of SHR were inhibited by central dopamine depletion. Antihypertensive treatment with hydralazine or captopril did not change behaviour, however. It is suggested that central dopamine systems may form a link between changes in behaviour of SHR and the development of hypertension in this strain. The changes in behaviour may underlie rather than be the result of the hypertension.