Prestained Protein Ladder, Broad Range (10-230 kDa) is a mixture of highly purified recombinant proteins covalently coupled to a blue dye that resolves into 12 sharp bands when electrophoresed. The protein concentrations are carefully balanced for even intensity. Both 80 kDa and 25 kDa bands have triple the intensity of other proteins and serve as reference indicators. The covalent coupling of the dye to the proteins affects their electrophoretic behavior on SDS-PAGE gels relative to unstained proteins (1). The apparent molecular weight of the Prestained Protein Ladder was determined on Invitrogen Novex 10-20% Tris-glycine SDS PAGE gels (1,2) by comparison to the Protein Ladder (NEB #P7703). The Prestained Protein Ladder is ideally suited for use in SDS-PAGE and western blotting applications. It allows continuous monitoring of protein separations during electrophoresis and also provides a quick and easy way to assess blotting efficiency (3).