Cancer can be viewed as a hierarchical system that is dependent on a small population of "cancer stem cells" with unlimited self-renewal potential for continued growth and propagation of tumors. The identity and nature of these cells remains enigmatic, but an improved understanding of their biology may allow for selective therapeutic targeting. A recent report by Jamieson et al. (2004) sheds new light on leukemia stem cells by identifying the cells with in vitro self-renewing properties in various phases of chronic myelogenous leukemia, and linking the self-renewal properties of this population to activation of β-catenin, a major effector of the canonical Wnt signaling pathway.