The 1H6 antibody reacts with CD34, an ~110 kDa glycoprotein on the surface of bone marrow-derived progenitors of hematopoietic and endothelial cells. In the bone marrow, 1-3% of cells are stained with 1H6 mAb; whereas peripheral blood leukocytes are not stained. Immunomagnetic depletion of lineage-committed leukocytes from bone marrow results in about three-fold enrichment of CD34+ cells. CD34+ hematopoietic progenitors may be mobilized to the peripheral blood by treatment with recombinant canine granulocyte colony-stimulating factor and stem-cell factor. Furthermore, CD34 is expressed on some canine leukemias. In the mouse, CD34 is also expressed on high endothelial venules (HEV) of lymph nodes and, in this form, functions as a ligand for L-selectin. CD34 expression on HEV of dog lymph nodes has been demonstrated with polyclonal anti-CD34 antibody.