Previous research has shown an association of both blood lead and dietary calcium with blood pressure (BP) in populations. We examined the relationship between blood levels and BP, the effect of calcium supplementation on blood lead, and whether the reported antihypertensive effect of calcium supplementation was related to any observed change in blood lead. BP was measured on four occasions, 1 week apart in 251 subjects. During this period, blood lead and erythrocyte protoporphyrin (EPP) levels were measured, as well as markers of calcium metabolism. In an intervention period, 142 patients were assigned to receive 1 g of calcium per day as calcium carbonate for 12 weeks; at the end of this period, blood lead and EPP were remeasured. In males, blood lead levels were significantly, directly related to BP; a 0.48 mumol/dL (10 micrograms/dL) increase in blood lead concentration was associated with a 5 mm Hg increase in systolic pressure. There was no relationship of blood lead levels to BP in females. EPP was unrelated to BP. Similarly, there was no relationship of blood lead levels to markers of calcium metabolism. With calcium supplementation, blood lead and EPP levels did not change significantly. We conclude that it is unlikely that modification of lead status explains any effects of calcium supplementation on BP.