The baseline observations in the Puerto Rico Heart Health Program during 1965–1968 involved blood pressure determinations, other measurements, and a 24-hour dietary recall in 7932 men aged 45–64 years. This extensive data base provided an opportunity to test the hypothesis that low calcium intake is related to increased blood pressure level. Among men without baseline coronary heart disease and not taking antihypertensive medication, there was an inverse relationship between milk consumption and definite hypertension in urban Puerto Rican men and older rural men. When data from all age and area groups had been averaged, a twofold increase in hypertension was found in subgroups who drank no milk compared to those who consumed over 1 quart of milk a day. Similar trends were found when an estimate of total calcium intake from food, principally from milk, was used. With multivariate analysis while known correlates of blood pressure were simultaneously considered, an independent effect persisted between milk consumption and blood pressure. These results appeared to confirm an inverse association between calcium and hypertension. It was still not possible to ascribe a causal relationship between calcium and blood pressure, however, due to the intricate network of covarying food intakes, the factors related to absorption or lack of absorption of calcium, and the possible role that unmeasured social and cultural factors may play in the observed relations.