In societies with several ethnic groups the prevalence of hypertension is abnormally high in black subjects. In addition, blacks are more susceptible to the consequence of high BP. Compared with whites plasma renin is low in blacks independently of age, the level of BP and dietary sodium consumption. No abnormal mineralocorticoid level has ever been consistently reported in blacks to account for their low renin. However potassium intake, prostaglandin and kallikrein excretions are low in blacks and black/white differences exist in the distribution of the restriction fragment length polymorphism at the gene loci for renin. It is hypothesised that the low renin and the propensity of blacks to hypertension result from elevated free cytosolic calcium. Indeed several factors inducing or associated with an increased cytosolic calcium cluster in blacks, e.g. sodium pump inhibition, high intracellular sodium concentration, low plasma ionised calcium, high parathyroid hormone. Furthermore, intensive calcium mobilisation from intracellular stores in response to circulating serum agonists as observed in skin fibroblasts of blacks might be contributive should it occur in all cells including vascular smooth muscle and juxtaglomerular cells.