We have previously shown that rats housed in individual metabolism cages develop arterial hypertension and that this can be prevented by adrenalectomy. In the present work the influence of adrenalectomy on blood pressure, heart rate and on fluid and electrolyte balance was investigated in rats with established isolation-induced hypertension. Seven days after adrenalectomy, systolic blood pressure was reduced to levels similar to those seen before the induction of hypertension; the fall in blood pressure was accompanied by tachycardia. It is likely that the reduction in blood pressure was partly due to volume depletion, since adrenalectomized rats showed reductions in fluid, sodium and potassium balance during the first week after operation. Over the following 3 weeks, blood pressure and heart rate returned to pre-operative hypertensive levels, associated with increasingly positive balances for fluid and sodium. Maintenance of elevated blood pressure in isolated rats following adrenalectomy is likely to have been aided by activation of the renin-angiotensin system, since infusion of saralasin caused profound hypotension in these circumstances, whereas it had a slight pressor effect in intact rats with isolation-induced hypertension.