FIG. 21B, for example, is an image of fluorescently labeled breast cancer cells that were spiked into a blood sample and then separated by dielectrophoretic retention on a dielectrophoresis chip (shown in FIG. 21A) after microfiltration of the blood sample. [0262] A method for enriching rare cells of the present invention that comprises at least one filtration step using a microfabricated fil