The gel cassettes provide a stiff backbone for the gel and membrane sandwiches. The hinged halves lock together for equal pressure across the gel. The grid design of the gel cassettes maximizes the open area for even transfers of gels up to 15 × 21 cm. The crucial element for uniform electrophoretic transfer, a uniform electrical field, is assured by spacing the electrode panels 10 cm apart and incorporating 140 cm of wire in an evenly-spaced pattern. For safety, the electrode panels are locked securely into the Transfer Unit, but can be easily removed for cleaning or replacement.