Even when chronic myelogenous leukemia is in remission, ‘sleeper cell,’ quiescent leukemic stem cells are maintained in microenvironments in the bone marrow. This maintenance is poorly understood. Researchers now describe how niche-specific expression of a particular chemokine by a particular type of bone marrow cell controls quiescence of these treatment-resistant leukemic stem cells. The chemokine is CXCL12, and the particular bone marrow cells expressing it are mesenchymal stromal cells.