Abstract: The present invention, in some embodiments, describes methods for selecting and enriching specific types of stem cells and/or progenitor cells from a sample containing at least two different types of stem cells and/or progenitor cells. In one embodiment, the method involves selecting and enriching cancer stem cells and/or cancer progenitor cells. In other embodiments, the invention involves improved methods for purging cancer cells from autologous or allogenic transplants prior to reinjection into a patient. In other embodiments, the invention describes improved methods to screen for the efficacy of drug candidate for affecting the function and/or viability of a specific type of stem cell or progenitor cell, for example a cancer stem cell. In this context, the inventive method can involve screening the effectiveness of chemotherapeutic agents in completely eliminating all cancer cells (i.e. mature cancer cells and cancer stem/progenitor cells).