Peripheral blood stem cells (PBSC) are used increasingly for autotransplantation in the treatment of acute leukemia, lymphoma, multiple myeloma, solid tumors such as ovarian and breast carcinoma. They are collected by leukaphereses during rapid hematopoietic recovery, following cytotoxic chemotherapy with or without administration of hematopoietic growth factors. We studied the clonogenic and cytokine-mediated expansion potential of CD34+ cells from mobilized PBSC. Low density mononuclear cells were processed using the CEPRATE LC CD34 KIT (CellPro). CD34+ purified cells, were cultured in suspension with 6 combined hematopoietic growth factors (IL1beta, IL3, IL6 at 100 U/ml and G-CSF, GM-CSF and stem cell factor at 10 ng/ml of each) for up to four weeks. Every week, cells were counted and CFU-GM assay was performed in a methylcellulose based medium. We have analysed the percentage of cells bearing CD34, CD33, CD38, HLA-DR, CD45RA, CD45RO antigens. Our results showed, that CD34+ cells were obtained with a purity of 92 +/- 2.3% and a yield of 71 +/- 10.7%. The majority co-expressed CD33 (57.76 +/- 34.16%) and CD38 (62.2 +/- 34%) antigens. These culture conditions, are necessary to obtain a fold increase of nucleated cells (377 fold at week 4), of CFU-GM progenitors (41.2 fold at week 3) and of CD34+ cell absolute number (10 fold at week 1) with an important differentiation of progenitors in particular myeloid progenitors.