The blood pressure responses of 19 mildly hypertensive (diastolic blood pressure 90-104 mmHg) individuals to treatment with either 1200 mg of elemental calcium supplementation or placebo were assessed weekly in a 6-month randomized, double-blind, placebo-controlled crossover study. Both groups showed a decrease in blood pressure (calcium treated: 6 +/- 12 mmHg systolic, 7 +/- 7 mmHg diastolic; and placebo controlled: 9 +/- 14 mmHg systolic, 9 +/- 8 mmHg diastolic). Differences between the two groups were not significant (P greater than 0.1). There were no adverse effects to either treatment. This study does not support the hypothesis that dietary calcium supplementation is more effective than placebo in reducing blood pressure in mildly hypertensive individuals.