This study aimed to identify which graft product subset of CD34+ cells might be the most predictive of early hematopoietic recovery following allogeneic peripheral SCT (allo-PBSCT). The relationship between the number of 'mature' subsets of CD34+ cells (CD34+/CD33+, CD34+/CD38+, CD34+/DR+ and CD34+/CD133-) and 'immature' subsets of CD34+ cells (CD34+/CD33-, CD34+/CD38-, CD34+/DR- and CD34+/CD133+) and early neutrophil and platelet engraftment were studied in a homogeneous series (for disease, pre transplant chemotherapy, conditioning regimen and GVHD prophylaxis) of 30 AML patients after allo-PBSCT from HLA-identical siblings. In our experience, the total CD34+/CD133+ cell number was inversely correlated with the days required for the recovery of 0.5 x 10(9)/l neutrophils (r=or-0.82, P=0.02) and platelets of 20 x 10(9)/l (r=or-0.60, P=0.06); this correlation was better than the total CD34+ cell dose and neutrophil (r=or-0.70, P=0.04) and platelet engraftment (r=or-0.56, P=0.07). We suggest that a high number of CD34+/CD133+ PBSC may be associated with faster neutrophil and platelet recovery; these findings may help to predict the repopulating capacity of PBSC in patients after allo-PBSCT, especially when a relatively low number of CD34+ cells is infused.