Abstract We explored the expression of a lymphocyte homing-associated cell adhesion molecule (H-CAM, CD44) on hematopoietic progenitors. We demonstrate that immature myeloid and erythroid leukemic cell lines stain intensely with monoclonal antibodies Hermes-1 and Hermes-3, which define distinct epitopes on lymphocyte surface H-CAM, a glycoprotein involved in lymphocyte interactions with endothelial cells. Using fluorescence-activated cell sorting (FACS), human marrow cells were fractionated into Hermeshi, Hermesmed, and Hermeslo populations according to the expression of both the Hermes-1 and Hermes-3 epitopes. Granulocyte-macrophage colony-forming unit and erythroid burst-forming unit precursors were found predominantly in the brightly positive fractions. Two-color FACS analysis confirmed that the My10 (CD34) positive populations of cells in bone marrow, which contain most of the progenitor cell activity, are brightly positive for Hermes-1. Finally, we demonstrate that among bone marrow cells, the highest levels of H- CAM are expressed on myeloid and erythroid progenitors as well as mature granulocytes and lymphocytes. Thus we provide evidence that molecules related or identical to the H-CAM homing receptor are expressed on marrow progenitor cells. H-CAM may contribute to progenitor cell interactions with marrow endothelial and stromal cell elements important to the maintenance and regulation of hematopoiesis.