In this paper the occurrence of bone in the human kidney in close association with parenchymatous stones will be described and its bearing on the theory of osteogenesis pointed out. The occurrence of bone in the kidney under experimental conditions has attracted much study since the original demonstration by Sacerdotti and Frattin1 (1901). It had long been demonstrated that following ligation of the renal artery or artery and veins, there occurs a massive necrosis of the renal substance, but not of the renal pelvis and ureter because of a different vascular supply. Extensive calcification of the necrotic renal tissue occurs within a few days (Blessig2), and bone1 develops some weeks later, forming chiefly and constantly beneath the mucosa of the pelvis with spurs extending into the remains of the kidney. The demonstration3 of a bone-stimulating effect of the epithelium of the renal pelvis makes it probable