Provided herein is an antagonist of GDF11 for use in a method for the treatment of anemia, ineffective erythropoiesis, beta thalassemia, or for increasing Orthochromatic Erythroblasts (Ery-C) in a patient, wherein the methods comprise administration of antagonists of Growth differentiation factor 11 (GDF 11; also known as bone morphogenetic protein 11 (BMP11)) to a subject in need of the treatment.