Hematopoietic progenitor cell transplantation is the treatment of choice for patients with malignant hematologic diseases. Neutrophil (NEUT) and platelet (PLT) counts are used to evaluate hematologic engraftment of transplanted patients. Recent-generation hematology analyzers offer an alternative way to evaluate immature peripheral blood (PB) cell fractions, which may also give an indication of hematopoietic recovery. The immature reticulocyte fraction (IRF) and immature platelet fraction (IPF) in PB samples may provide early indicators of transplant success. We evaluated the predictive value of IRF and IPF for the hematologic recovery of 46 adult patients undergoing allogeneic PB progenitor cell transplantation. We observed that IRF recovery anticipated by 4 days compared with NEUT recovery (11 vs 15 d) and IPF by 2 days compared with PLT (10 vs 12 d). The recovery was different for patients undergoing a nonmyeloablative regimen (NMA); we observed an early IRF recovery by 5 days compared with NEUT (10 vs 15 d) and a IPF compared with PLT recovery by 2 days (9 vs 11 d). We also observed significant correlations between NEUT and PLT recovery with recoveries of the new parameters IRF and IPF. We concluded that IRF and IPF predicted hematopoietic recovery. For allografted patients after NMA regimens, prediction was even more clinically relevant. These immature fractions open new perspectives for monitoring patient transfusion support through the posttransplantation recovery.