In order to study the erythropoietic function of the bone marrow in renal anemia and influences of azotemia on the erythropoietic function, bone marrow culture in fluid medium was performed on patients with renal diseases and healthy individuals. The rate of erythrocyte increase, hemoglobin increase, rate of nucleated cell increase and percentage of erythroblasts were measured. The results are summarized as follows. 1) Enhancement of the erythropoietic function was observed, when normal human serum was added to the medium culturing marrow specimens from patients with acute glomerulonephritis or chronic glomerulonepbritis showing a mild elevation of NPN.2) In patients with chronic glomerulonephritis with azotemia or patients with uremia, an addition of normal human serum to the culture medium had no effect on the already depressed erythropoietic function of the bone marrow. 3) The bone marrow erythropoietic funotion of healthy individuals was markedly decreased, when azotemic serum was added to the fluid medium. It has thus become clear that azotemia in chronic renal insufficiency depresses the marrow erythropoietic function of healthy persons. The cultured bone marrow from patients with a prolonged azotemia resulting from chronic renal insufficiency, therefore, shows depression of the erythropoietic function.