Erythropoietin‐Stimulated Proliferation of Human Red Cell Precursors in Vitro

S ummary . A liquid culture system is described that supports human erythropoiesis in vitro. Replication and maturation of red cell precursors in bone marrow from normal subjects and from patients with various disturbances of haemopoiesis were sustained in culture for periods up to 2 weeks. Added erythropoietin stimulated erythroid precursor DNA synthesis and cell replication. The erythropoietin effect was inhibited by a rabbit antibody to human erythropoietin. The culture system provides a means to study directly normal and abnormal human erythropoiesis in vitro.