Abstract: A protein purification system employs a pretreatment device which operates in concert with an electrophoretic purification device to separate and retrieve a large volume of highly purified proteins or other products from a mass of crude cellular extract. The pretreatment device causes the products to migrate horizontally through a series of cassettes and chambers at a relatively rapid rate determined by the size of the products to produce a crude mixture of products amenable to further purification. The purification device employs continuous vertical gel electrophoresis to separate the crude mixture into the highly purified products in large volumes and at a high rate without cooling. The electrophoretic purification device is also durable, easy to construct and use, and can be easily adjusted to vary the amount of matrix or gel through which the products must migrate, thus varying the amount of available purification.