Embodiments of the present invention are directed to uses of Interleukin-12 (IL12) in enhancing or stimulating hematopoietis to yield hematopoietic recovery in a mammal in need. Particular embodiments of the invention are directed to uses of IL-12 as an adjuvant therapy to alleviate the hematopoietic toxicities associated with one or more treatment regimens used to combat a disease state. Other embodiments include uses of IL-12 to ameliorate various hematopoietic deficiencies. Still other embodiments are directed to uses of IL-12 for in-vivo proliferation of hematopoietic repopulating cells, hematopoietic progenitor cells and hematopoietic stem cells. Other disclosed embodiments are directed to uses of I1-12 for bone marrow preservation or recovery.