The aim of this study was to explore the capacity of human CD34+ stem cells from umbilical cord blood to differentiate into endothelial cells, in culture, after addition of specific growth factors, and also to compare their behaviour with that of endothelial cells obtained from human umbilical vein (HUVEC). CD34+ cells were positively selected using immunomagnetic beads (Dynal, Oslo-Norway). Isolated cells were grown in medium containing rh Stem Cell Factor (50 ng/ml), rh GM-CSF (10 ng/ml), rh IL-3 (10 ng/ml), 1% methylcellulose in Iscove MDM, 30% FCS, supplemented with antibiotics and 0.75 mg/ml Endothelial Cells Growth Supplement (ECGS). The cells were seeded in 24-well plates and incubated at 37 °C in an atmosphere with 5% CO2. After 3 days of culture, beside 0.75 mg/ml ECGS, the medium was also supplemented with Epidermal Growth Factor (EGF; 0.1 ng/ml) and beta-Fibroblast Growth Factor (beta-FGF; 1 ng/ml). In another experiment, ECGS was replaced by VEGF (10 ng/ml). In both experiments, after 10-15 days of culture, the cells formed small clusters of adherent, flat, and elongated cells, finally forming a monolayer that filled the plate. Immunocytochemical analysis revealed the presence of CD31 surface antigen and von Willebrand factor. Flow cytometric analysis of ECAM expression of the CD34+ cells displaying morphological alterations showed that 9.65±0.2% of the studied cells expressed CD54/ICAM-1 and 7.73±0.3% expressed CD106/VCAM. Endothelial cells obtained from umbilical vein presented a similar expression of the studied endothelial adhesion molecules before the action of TNF. After 10 h incubation with TNF, the expression of CD54 and CD106 was not significantly increased on cells obtained from CD34+ stem cells (10±0.2 and 7.9±0.1%, respectively), whereas HUVEC expressed CD54 and CD106 in proportion of 43±2 and 29±1.4%, respectively. These data demonstrate that a fraction of CD34+ cells develop some endothelial cell characteristics when cultured with ECGS or VEGF, but they are functionally different from HUVECs.