The present invention provides methods of using Bv8 and EG-VEGF polypeptides and nucleic acids to promote hematopoiesis. Also provided herein are methods of screening for modulators of Bv8 and EG-VEGF activity. Furthermore, methods of treatment using Bv8 and EG-VEGF polypeptides or Bv8 and EG-VEGF antagonists are provided.