The relation between dietary calcium and blood pressure was examined in 1,928 men, ages 40-69 years, from five geographic and two occupational populations in Japan. Dietary calcium intake was estimated using 24-hour dietary recall in systematic samples of participants of population-based cardiovascular surveys from 1983 to 1987. The means of daily calcium intake of the study populations ranged from 449 to 695 mg, approximately 300 mg lower than the recommended US dietary calcium intake. Linear regression analyses were used to examine the relation between dietary calcium and blood pressure within each population, controlling for age, body mass index, alcohol consumption, and sodium intake. Total calcium intake was inversely associated with the systolic blood pressure level in each population, and the pooled estimate of the regression coefficients for millimeters of mercury of blood pressure per 100-mg increase in calcium intake was -0.54 (95% confidence interval -0.89 to -0.19). The inverse association between calcium intake and diastolic blood pressure was less consistent, and the pooled estimate did not reach statistical significance (-0.10, 95% confidence interval -0.34-0.14). Inverse associations existed for both dairy and nondairy food sources of calcium when analyzed separately, and the association was significant only for dairy calcium. Although a causal relation between dietary calcium and blood pressure cannot be established, these results suggest a possible public health implication in Japan of increasing calcium intake for the prevention and control of hypertension, where average dietary calcium intake is low.