Intravascular destruction of erythrocytes sufficient to produce hemolytic anemia occurs with incompetent prosthetic heart valves. Renal hemosiderosis results from chronic intravascular hemolysis. Increased urinary iron loss eventually produces an iron-deficiency state even in the presence of renal hemosiderosis. Deferoxamine mesylate, an iron-chelating agent, increases the urinary iron excretion in this combination of circumstances, suggesting that it removes iron from the kidney. A compensated hemolytic state has occurred in some of these patients after iron therapy, and reoperation was thereby avoided. Elevated serum lactic dehydrogenase values indicate hemolysis and remain unchanged with iron therapy. Iron therapy had no influence on erythrocyte survival.