Abstract: A casting apparatus for receiving electrophoretic gel trays is disclosed. The casting apparatus includes a pair of spaced apart seal elements which are movable with respect to one another to provide one or, more openings of varying size to receive a corresponding gel tray therein. The open ends of the gel tray are sealed by the seal elements so that hot argrose or polyacrylamide gel may be poured into the gel tray for forming a gel layer of predetermined thickness. The seal elements are maintained in sealing engagement with the open ends of the gel trays by means of a rod frictionally engaged between a portion of the housing forming the casting apparatus and one of the seal elements.