Bone marrow–derived mesenchymal stem cells (BM-MSCs) in the marrow stroma provide a scaffold for hematopoiesis. Chemokine stromal cell–derived factor-1 (SDF-1) and its receptor CXCR4 have been shown to affect the engraftment of hematopoietic stem cells. However, little is known about SDF-1/CXCR4’s functions in regulating BM-MSCs in humans. As an initial step toward this issue, we have evaluated expression of SDF-1/CXCR4 in the BM-MSCs from a cohort of adolescents and young adults with acute lymphoblastic leukemia (ALL). We found a decrease of the CXCR4 level and an increase of the SDF-1 level in these MSCs of ALL. Moreover, cell migration appeared to be impaired in the MSCs of ALL. These changes were reversed by chemotherapy. Taken together, alteration of SDF-1/CXCR4 expression could be potentially developed as biomarkers for monitoring the effectiveness of chemotherapy.