This invention relates generally to the field of cell separation or isolation. In particular, the invention provides a method for separating cells, which method comprises: a) selectively staining cells to be separated with a dye so that there is a sufficient difference in a separable property of differentially stained cells; and b) separating said differentially stained cells via said separable property. Preferably, the separable property is dielectrophoretic property of the differentially stained cells and the differentially stained cells are separated or isolated via dielectrophoresis. Methods for separating various types of cells in blood samples are also provided. Centrifuge tubes useful in density gradient centrifugation and dielectrophoresis isolation devices useful for separating or isolating various types of cells are further provided.