Stem cells and cancer stem cells are 2 distinct, evolving, and promising areas of research. Hematopoietic stem cells are already used in the treatment of bone marrow failure and hematologic malignancies, and there is now great interest in isolating stem cells from other organs for use in replenishing damaged tissue in the heart, brain, bones, and other organs and structures. In contrast, cancer stem cells, a newly recognized component of some cancers, have some properties of pluripotent stem cells in that they replicate without normal cell cycle regulation and apoptosis. Moreover, they are naturally resistant to chemotherapy because of drug-exuding pumps, DNA repair proteins, and dormancy; thus, these cells are now suspected to be the root cause of relapse and metastasis after conventional therapies in some malignancies, especially leukemia. Targeting cancer stem cells in addition to cancer cells may therefore lead to better eradication of cancer than is presently possible.