An electrooptical method is disclosed for quantifying the motility response of cells to external stimuli, wherein a target cell population (formed as a function of said response) is subsequently optically differentiated by the addition of an optical differentiation solution, and whereby the targeted cell population becomes more or less detectable to an electrooptical reading device. The method can be used to perform chemotactic assays. For such and other purposes, the method can be performed utilizing high throughput robotic automation.