Methodology has been developed that enables virtually complete purification and recovery of early hematopoietic progenitors from human adult blood, a minority of which is multipotent and endowed with self-renewal capacities, i.e., exhibits stem cell properties. This report briefly reviews: (i) the key steps involved in the progenitor purification and assay procedure; (ii) the characterization of "pure" progenitors at the level of membrane antigen pattern and response to HGFs; (iii) the development of a liquid suspension culture for the pure progenitors, which allows synchronized and selective erythroid or GM differentiation, and hence may be utilized for the analysis of molecular mechanisms underlying early and late stages of hematopoiesis; (iv) the study of the expression and modulation of HGFRs expressed on progenitors.