To study the effect of dietary salt restriction and supplementation on blood pressure of elderly subjects, we performed a randomized, placebo-controlled, double-blind, crossover trial. Seven healthy subjects living in a long-term care facility, with a mean age of 85 and normal to borderline-hypertensive blood pressures, completed a 16-week protocol. During the double-blind cycles, subjects consumed either a low sodium (43 mmol/day) or a high sodium diet (175 mmol/day) for four weeks supplemented with placebo or salt capsules, with crossover to the other diet. Sitting diastolic blood pressure was significantly lower during the low sodium diet (69.86 mmHg +/- 3.80 vs 78.71 mmHg +/- 3.99, P less than .01), with all subjects showing decreases. Supine plasma renin activity and plasma aldosterone were significantly lower during the high sodium diet. Both low and high sodium diets were well-tolerated by subjects. Symptomatic postural hypotension and hyponatremia were not observed. We conclude that old-old subjects with borderline hypertension demonstrate salt-dependent increases in blood pressure. Without additional supportive studies, however, these results should not be generalized to any specific cohort of elderly individuals.