Inhibitors of erythropoiesis in patients with aplastic anemia.

An inhibitor of erythropoiesis was found in the urine of patients with aplastic anemia. The inhibitor was concentrated with kaolin and separated from erythropoietin by subsequent fractionation with alcohol and gel filtration on Sephadex G-100 and DEAE-Sephadex A-50. The inhibitor blocked the effect of erythropoietin (standard C) when injected into mice with hypoxic polycythemia 3 H before or along with exogenous erythropoietin; partial neurtralization of standard C also was observed on incubation with the inhibitor.