1. Blood pressure, plasma renin concentration, exchangeable body sodium, plasma volume and extracellular fluid volume were measured in five patients on maintenance haemodialysis for end-stage renal disease in whom hypertension was relatively easy to control by the combination of dialysis and restriction of salt intake. Measurements were made on three occasions: on a free salt intake the day before dialysis; on a low salt intake the day after dialysis; on a free salt intake the day before dialysis after nephrectomy.
2. The fall of blood pressure after haemodialysis and salt intake restriction was accompanied by a decrease of exchangeable body sodium and body fluids while plasma renin concentration increased. The fall of blood pressure after bilateral nephrectomy was accompanied by a fourfold decrease of plasma renin without any change of the other variables.
3. The hypertension of these patients might thus be considered ‘salt and water dependent’ or ‘renin dependent’ according to the means used to decrease blood pressure.