A substantially enriched mammalian hematopoietic cell subpopulation is provided, which is characterized by progenitor cell activity for myeloid lineages, but lacking the potential to differentiate into lymphoid lineages. This population is further divided into specific myeloid progenitor subsets, including a common myeloid progenitor cells (CMP), megakaryocyte/erythroid progenitor cells (MEP) and granulocyte/monocyte lineage progenitor (GMP). Methods are provided for the isolation and culture of these subpopulations. The CMP population gives rise to all myeloid lineages, and can give rise to the two additional and isolatable progenitor populations that are exclusively committed to either the erythroid/megakaryocytic or myelomonocytic lineages. The cell enrichment methods employ reagents that specifically recognize Thy-1; and IL-7R.alpha., in conjunction with other markers expressed on lineage committed cells. These cells give rise to a variety of myeloid cells, including megakaryocytes, granulocytes, dendritic cells and erythroid cells, as evidenced by their growth and differentiation in vitro and in vivo.