Isonatric (high sodium) dialysis has several advantages, including relative freedom from cramps. The diastolic blood pressures and body weights of nine originally hypertensive patients on maintenance haemodialysis have been recorded for 15 months throughout alternating periods on isonatric (145 mEq/l) and low (132·5 mEq/l) dialysate sodium concentration. Isonatric dialysis resulted in a temporary 1-2 kg increase in mean pre-dialysis weight, requiring increased ultrafiltration. This coincided with a slight increase in mean pre-dialysis diastolic blood pressure which was corrected when post-dialysis body weights were lowered to compensate for the increased weight gain between dialyses. Once the ‘ideal’ individual post-dialysis body weight for each patient was established, pre-dialysis diastolic pressures less than 90 mmHg were achieved routinely. Ten subsequent patients who have never received low sodium dialysis also have well controlled pressures. These findings are contrary to the orthodox view that low sodium dialysis is mandatory to avoid hypertension.