Human pluripotential stem cells (PSC) are currently the target for transplantation attempts and genetic manipulation. We have therefore investigated the frequency and the expansion potential of PSC's in different types of blood samples. CD 34+ cells were thus obtained from human bone marrow (BM), as well as from peripheral blood (PB) and cord blood (CB) samples. After immuno-magnetic separation the highest yields of CD 34+ cells were from BM (1.08-2.25%) and CB (0.42-1.32%) while PB samples gave much lower values. Suspension cultures of PSC's from the three sources were then set up, in the presence of combinations of haemopoietic growth factors. A remarkable amplification of the nucleated cell pool was observed reaching a maximum between 10 and 15 days of culture; earliest and maximum expansion (up to 220-fold) was achieved when Erythropoietin (Epo) was added to the culture medium, but this resulted in reduction of colony-forming cells and differentiation into erythroid progenitors. Clonogenic tests for BFU-E's derived colonies showed a peak value at 5 days of liquid culture. Further studies are advisable to establish the best cytokine combination for a valuable ex vivo expansion, coupled with preservation of stem cell properties.