Abstract: The invention is an apparatus and method for performing the Western Blot Assay and other assays. The invention includes a tray within which multiple samples can be assayed with a minimum of operator attention. The tray that is desirably used with the apparatus is multichambered and can be alternately agitated and drained according to drive cards and/or other controls such as electronic controls. The tray is designed in such a way that reagents and washing fluids, which are added sequentially and then cleared, do not back flow into the chambers of the tray.