A substantially enriched mammalian hematopoietic cell subpopulation is provided, which is characterized by progenitor cell activity for lymphoid lineages, but lacking the potential to differentiate into myeloid and erythroid lineages. Methods are provided for the isolation and culture of this common lymphoid progenitor cell (CLP). The cell enrichment methods employ reagents that specifically recognize CDw127 (IL-7 receptor .alpha.); CD117 (c-kit) protein, in conjunction with other markers expressed on lineage committed cells. The murine cells are also characterized as expressing low levels of sca-1 (Ly-6E and Ly-6A). The CLPs are predominantly cycling, blast cells. These cells give rise to B cells, T cells and natural killer cells, as evidenced by their growth and differentiation in vitro and in vivo.