SDF-1, a stromal cell-derived factor, is a highly effective lymphocyte chemoattractant. It is produced by bone marrow stromal cells and attracts 10-fold more lymphocytes than previously described chemoattractants. SDF-1 acts on lymphocytes and monocytes but not neutrophils in vitro and is a highly efficacious and potent mononuclear cell attractant in vivo. It induces intracellular actin polymerization, a process essential for cell motility. SDF-1 is constitutively expressed in a broad range of tissues and may play a role in immune surveillance rather than inflammation. SDF-1 is a member of the chemokine family, showing sequence homology to both CC- and CXC-chemokines. It is more conserved than other chemokines and may represent a primordial chemokine. SDF-1 is highly effective in attracting mononuclear cells in vivo, with a greater number of cells infiltrating than other chemokines. It is also less potent in vitro than some other chemokines but highly effective in vivo. SDF-1 is produced by bone marrow stromal cells and may be involved in the trafficking of lymphocytes and monocytes to this site. Its tissue distribution suggests a role in lymphocyte recirculation and the basal recruitment of monocytes in tissue mononuclear phagocyte turnover rather than in inflammation. SDF-1 is constitutively expressed in various tissues and may have broader importance beyond bone marrow. It is not affected by inflammatory stimuli, unlike most other chemokines. SDF-1's unique properties make it a distinct chemokine, possibly representing a new subfamily.SDF-1, a stromal cell-derived factor, is a highly effective lymphocyte chemoattractant. It is produced by bone marrow stromal cells and attracts 10-fold more lymphocytes than previously described chemoattractants. SDF-1 acts on lymphocytes and monocytes but not neutrophils in vitro and is a highly efficacious and potent mononuclear cell attractant in vivo. It induces intracellular actin polymerization, a process essential for cell motility. SDF-1 is constitutively expressed in a broad range of tissues and may play a role in immune surveillance rather than inflammation. SDF-1 is a member of the chemokine family, showing sequence homology to both CC- and CXC-chemokines. It is more conserved than other chemokines and may represent a primordial chemokine. SDF-1 is highly effective in attracting mononuclear cells in vivo, with a greater number of cells infiltrating than other chemokines. It is also less potent in vitro than some other chemokines but highly effective in vivo. SDF-1 is produced by bone marrow stromal cells and may be involved in the trafficking of lymphocytes and monocytes to this site. Its tissue distribution suggests a role in lymphocyte recirculation and the basal recruitment of monocytes in tissue mononuclear phagocyte turnover rather than in inflammation. SDF-1 is constitutively expressed in various tissues and may have broader importance beyond bone marrow. It is not affected by inflammatory stimuli, unlike most other chemokines. SDF-1's unique properties make it a distinct chemokine, possibly representing a new subfamily.