We assessed the development of an adherent stromal layer in peripheral blood progenitor cells (PBPC) collections of 17 patients with solid tumors and hematological malignancies (n = 38), as well as in normal and disease-free bone marrow samples (n = 14). Light-density mononuclear cells from peripheral blood leukapheresis maintained in long term culture (LTC) conditions for at least 3 weeks failed to develop a stromal layer as was observed in all bone marrow samples. We found no differences with regard to CFU-GM growth, CD34+ percentage or cytological morphology. Our results indicate that spindle-shaped fibroblastoid cell progenitors present in the bone marrow are not mobilized towards peripheral blood by chemotherapy and/or growth factor stimulation, contrasting with hematopoietic progenitors, which, as is well known, are able to circulate. The absence of stromal progenitors in PBPC autografts does not appear to be relevant for a successful hematopoietic engraftment.