The increase in total body sodium and hyperactivity of the renin-angiotensin system plays a major part in hypertension in patients underdoing chronic dialysis. After sodium depletion most patients become normotensive. Their hypertension seems to be due to sodium overload but it is favoured by insufficient inhibition of renin secretion. Some renin hypertensive, hypersecretion of renin is the main factor in these cases but its effect is aggravated by the sodium overload. Other factors may play a role as suggested by the studies of hypertensive patients after bilateral nephrectomy. However, their roles and mechanisms are unknown at present.