The CD34(+) compartment of grafts for clinical allogeneic hematopoietic cell transplantation (HCT) is very heterogeneous. It contains hematopoietic stem cells and several different progenitor cell populations. This study assesses (1) the content of these populations in clinical grafts from G-CSF-mobilized PBMCs, BM and cord blood, (2) the functional correlation of the graft composition with time to engraftment of neutrophils, platelets and reticulocytes and (3) donor age-related changes. Quantitative flow cytometry showed that the distribution of the progenitor subsets differed significantly between the graft sources and that donor age-related changes occur. In patients after myeloablative allogeneic HCT, accelerated platelet and reticulocyte engraftment correlated with the content of common myeloid and/or megakaryocyte erythroid progenitors in the graft. These findings show that a better understanding of the progenitor compartment in human hematopoietic grafts could lead to improved strategies for the development of cellular therapies, for example in situations where platelet engraftment is delayed.