It is believed that cancer stem cells (CSCs) are precursors for the formation, development, and recurrence of malignant tumors. However, it has proven difficult to isolate and enrich these rare, undifferentiated cells from heterogeneous tumor masses. With some existing reports and preliminary results in mind, we hypothesized that the mitochondrial membrane potential within a tumor mass was heterogeneous and could be used as a tool to isolate and enrich CSCs.