To define an optimal regimen for mobilizing blood-derived progenitor cells from healthy donors for allogeneic transplantation, we have studied the early and lineage-committed CD34+ subsets in the leukapheresis products after mobilization with G-CSF (10 micrograms/kg/d), GM-CSF (10 micrograms/kg/d), and the combination of G-CSF and GM-CSF (G/GM, 5 micrograms/kg/d of each). We used three color and five dimensional flow cytometry with a panel of monoclonal antibodies against CD3, CD7, CD10, CD11b, CD15, CD33, CD34, CD38, CD45, CD61, and CD71. As reference, we also analyzed CD34+ subsets in samples from umbilical cord blood (UCB) and from adult bone marrow (BM). The level of total CD34+ cells was 0.04 +/- 0.03% (mean +/- SD) in peripheral blood at baseline, and reached a maximum on day 5 or day 6 of administration of growth factors. The percentages of CD34+ cells in the leukapheresis products were 1.06 +/- 0.37% (mean +/- SD) with G-CSF mobilization, 0.35 +/- 0.24% with GM-CSF, and 0.92 +/- 0.61% with the combination of both. Among the CD34+ subsets, the percentage of cells that were CD34+/CD38- was highest in UCB (7.18 +/- 5.58%) and lowest in G-CSF mobilized peripheral blood (0.80 +/- 0.22%), whereas GM-CSF or G/GM mobilized products gave rise to intermediate levels (4.43 +/- 3.40%, 3.61 +/- 2.42%, respectively). The differences between G/GM and G-CSF, between UCB and G-CSF, or between UCB and BM are significant. The absolute numbers of CD34+/CD38- and CD34+/CD38-/HLA-DR+ subsets are also significantly higher in the G/GM mobilized products than in G-CSF products. The cloning efficiency of G/GM mobilized CD34+ cells was 2 times higher than that of G-CSF mobilized CD34+ cells, albeit the difference was statistically marginal. The profile of CD34+ subsets mobilized by the combination of G/GM approaches that found in UCB. Our data illustrate that different growth factors and regimens can preferentially mobilize different CD34+ subsets from normal donors, and that the combination of G-CSF and GM-CSF might be an optimal regimen.