An apparatus for preparative gel electrophoresis is described. The maximum load of protein is about 1 gm for a multicomponent sample. The resolution is close to that obtained in analytical gel electrophoresis runs. The substances migrate from the gel into a granular bed from which they are displaced by a buffer flow that transfers them to a fraction collector. The cooling tubes are placed inside the gel chamber. These are therefore in very good contact with the gel, providing efficient and uniform cooling. The importance of a good temperature control in polyacrylamide gel electrophoresis is discussed. The apparatus is manufactured by LKB-Produkter AB, Stockholm, Sweden. © 1968.