Diagrammatic representation of the flow-based adhesion assay incorporating an hydraulic-driven perfusion system allowing the collection of buffer perfused over adherent cells. The master syringe (driven by a Harvard syringe pump) expels water into one of three slave syringes. Switching between the slave syringes is via electronic valves. Each slave syringe is mounted back to back with and drives a perfusion syringe containing a different perfusate (wash buffer, cell suspension, or chemotactic agent). Output from the perfusion syringes is selected via a 4-way teflon tap, the common outlet of which is attached to a microslide containing the adhesive substrate. The microslide sits on the stage of a video-microscope. Perfused medium for analysis is collected from the distal end of the microslide into micro-centrifuge tubes.