A method is provided for use with extracted blood, including (a) applying blood to a first gradient suitable for selecting first-pass cells having a density less than 1.077 g/ml； (b) applying the first-pass cells to a second gradient suitable for selecting second-pass cells having a density between 1.055 and 1.074 g/ml； (c) increasing the number of cells having a density between 1.055 and 1.074 g/ml, by culturing the second-pass cells for a period lasting between 3 and 30 days； and (d) identifying endothelial progenitor cells in the cultured cells. Other embodiments are also described.
