Abstract: Non human animal models are provided for diseases involving erythroid function, particularly myeloproliferative disease. The models are useful for testing and screening of biologically active agents that affect erythropoiesis, and erythroid function. In the animal models of the invention, a hematopoietic stem or progenitor cell (HSC) population that has been genetically altered by the introduction of a mutant JAK2 coding sequence is transplanted into an immunocompromised, xenogeneic, non-human recipient. The recipient animal is engrafted with the cell population at a high frequency, and develops a myeloproliferative disorder characterized by polycythemia.