Abstract: A vertically oriented gel electrophoresis apparatus having a support structure for supporting in a generally vertical plane a gel plate assembly, including a pair of upright side members, a support plate lying in a vertical plane and extending between the side members, a lower buffer tank for supporting the gel plate assembly between the side members, and an upper buffer tray having a sealing gasket on one side thereof which is engageable with the gel plate assembly adjacent the upper edge thereof upon movement of the upper tray into engagement with the gel plate assembly, to seal against leakage of buffered solution disposed in the upper tray. The upper tray is moved into sealing engagement with the gel plate assembly and away therefrom by a cam disposed in cam slots in the sides of the upper tray and operated by a handle disposed externally of the side members and connected to the cam by a shaft passing through the side members.