We investigated the modulation of CXCR4 expression by cytokines, dexamethasone, and hypoxia in myeloma cells in vitro. Tumor necrosis factor-alpha (TNF-), transforming growth factor-beta1 (TGF-β1), and vascular endothelial growth factor (VEGF) enhanced CXCR4 expression in RPMI8226 cells. In the myeloma cell lines examined and primary bone marrow (BM) CD138+ cells, dexamethasone enhanced CXCR4 expression both in the cytoplasm and on the cell surface, while downregulating SDF-1 expression and secretion in BM stromal cells. Incubation of cells under hypoxic conditions (1% O₂) also induced upregulation of CXCR4 in the cytoplasm and on the cell surface and enhanced chemotaxis in response to stromal cell-derived factor-1 (SDF-1). Cell surface CXCR4 expression was more prominent in annexin V-positive apoptotic cells. Given the roles of the SDF-1/CXCR4 axis in the development and progression of myeloma, CXCR4-downregulating agents may enhance the antitumor effects of dexamethasone.