The renal distribution of calcium was measured at necropsy in adult subjects from populations with and without a tendency to calcium stone formation. The mean concentration of calcium in tissue from the papilla tip was significantly higher than that from the base of the medulla in both populations, confirming the presence of a calcium concentration gradient in the adult human renal medulla. Both the mean concentration of calcium in the papilla tip, and the mean calcium concentration gradient in the medulla, were significantly higher in the white South Africans of European descent than in the Bantu in South Africa. Renal stone disease is rare in the latter. The possible association between high concentrations of calcium in the papilla tip and the tendency to calcium stone formation is discussed in terms of the renal handling of calcium and the aetiology of the calcium-containing stone.