OBJECTIVE To assess the effects of 80 mmol/day reduction in dietary sodium intake on clinic and 24-h ambulatory blood pressure in elderly hypertensive subjects. METHODS Double-blind, randomized, placebo-controlled, crossover trial lasting 10 weeks, following a 4-week run-in period. METHODS Seventeen untreated subjects with essential hypertension [systolic blood pressure (SBP) > or = 160 mmHg and/or diastolic blood pressure (DBP) > or = 95 mmHg], mean age 73 years (range 66-79). METHODS Subjects had clinic blood pressure and 24-h urinary electrolyte excretion measured while on their normal diet. Following a 4-week run-in period on a reduced-sodium diet (80-100 mmol/24 h) subjects entered a 10-week crossover trial of 80 mmol/24 h sodium supplement or matching placebo while continuing on the reduced-sodium diet. METHODS The within-patient change in clinic and 24-h ambulatory blood pressures at the end of each intervention period. RESULTS Mean urinary sodium excretion at the end of the run-in phase rose during the high sodium intake phase and was reduced significantly at the end of the low sodium intake phase. There was a significant reduction in clinic supine SBP between the high- and low-sodium phases. There was no significant change in standing SBP, supine or standing DBP or pulse rate between phases. There was a non-significant reduction in mean 24-h SBP and DBP on the low sodium intake. At the end of the low-sodium phase there was a significant increase in plasma renin activity and aldosterone levels, but no change in plasma electrolytes. CONCLUSIONS Overall, moderate sodium restriction in elderly hypertensives resulted in a significant fall in clinic supine SBP only, although marked differences in intersubject responses were found. Moderate sodium restriction may be of benefit in only some elderly hypertensive subjects as part of a non-pharmacological regimen for blood pressure reduction.