Cd34+ Cells,Present at a Frequency of 0.18 ± 0.052% Among Leukocytes from PeRipheral Blood(Pb), Can Be Rapidly and Efficiently En- Riched to a Frequency of 38.6-87.1%(&4*4 By High-Gradient Magnetic Cell Separation (Macs) For Immunopheno- Typing,Characterization In Colony-FormIng Cell Assays, and Further PuRification Tohomogeneity (>98%) By Multiparameter Fluorescence-Activated Cell Sorting(Facs). Enriching Pb-Cd34+ Cells For Immunophenotyping Allows the Detection Ofsmall Subpopulations, ExPressing the B-Cell Antigens Cd10, Cd19, and Cd20, Thet-Cell Antigens Cd45ra and Cd7, and a Small Subpopulation ExPressing Highlevels of Cd34 Which Mostly Coexpress Cd19 Cd20 ; and Cd38. All Pb-Cd34 + Cells Express Elevatedlevels of Cd71 (Transfer-Rin Receptor), With a Subpopulation of High Expressingcells, and Cd38. some Cells Express Cd33. Macs-Enriched Pb-Cd34+Cells Show "Normal" Hematopoie-Tic Colony Formation In Vitro. Theease and Efficiency of Purification of Large Numbers of Cd34+ Cellsfrom Pb By Macs Is Not Only Relevant For the CharActerization of Migratingstem Cells But Also Opens New Possibilities For Stem Cell Transplantation &Genetic ManipulaTion of the Hematopoietic System.