Abstract: Two-dimensional gel electrophoresis apparatus includes an electrophoresis zone having four edges defined by a plurality of electrodes. A pair of opposed edges are defined by groups of discrete electrodes. Discrete electrodes within each group are electrically isolated from each other while the other pair of opposed edges are used to generate an electrical field. As a result, the electrical field is less distorted than would be the case if each edge was defined by a single elongate electrode. The apparatus can be provided as a cassette with electrodes configured to guide gas generated during electrolysis out of the cassette through apertures, to reduce the build up of combustible gases.