Methods for enhancing or stimulating hematopoiesis including the step of administering Interleukin-12 (IL-12) to yield hematopoietic recovery in a mammal in need. Preferred methods include the step of administering 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 methods include administering IL-12 to ameliorate various hematopoietic deficiencies. Still other methods are directed to uses of IL-12 for in-vivo proliferation of hematopoietic repopulating cells, hematopoietic progenitor cells and hematopoietic stem cells. Other disclosed methods are directed to uses of IL-12 for bone marrow preservation or recovery.