The proton-coupled folate transporter (PCFT) knockout mouse develops systemic folate deficiency after birth and, if untreated, succumbs within 10 to 12 weeks. Macrocytic anemia and pancytopenia with accumulation of immature erythroblasts in bone marrow and spleen are observed in these animals. Serum levels of erythropoietin (EPO), thrombopoietin (TPO), and soluble transferrin receptor (sCD71) are increased. Plasma total homocysteine (tHcy) and total iron (tFe) are also increased. PCFT^−/− mice are a model for human hereditary folate malabsorption. Professional illustration by David Schumick.