A gel enclosure and buffer tank for vertical slab gel electrophoresis are disclosed. The gel enclosure is formed from two flat plates, one of which contains angled troughs extending off to one side to serve as extensions of the sample wells, thereby increasing the volumetric capacity of each sample well, and improving the ease of loading it with sample. The buffer tank is constructed in such a manner as to hold one flat plate of the gel enclosure in contact with a flat heat transfer wall of the buffer tank, with cooling applied to the outside of the wall by thermoelectric means. Buffer solution below the gel enclosure is also cooled by the cooling wall, and bubbles generated at an electrode, also positioned below the gel enclosure, agitate the cooled buffer solution, extending the cooling effect over the entire surface of the other flat plate of the gel enclosure.