AbstractDiagonal gel electrophoresis is a form of two‐dimensional analysis useful for investigating the subunit composition of multisubunit proteins containing interchain disulfide bonds. Proteins are electrophoresed in the first dimension in a slab or tube gel under nonreducing conditions. The proteins are then reduced in the gel and this piece of gel is layered onto a second gel and electrophoresed. In the second gel, the proteins migrate at right angles to their original, first‐dimension migration. The majority of cellular proteins are not disulfide‐linked and will fall on the “diagonal” in this system; that is, they migrate approximately equal distances in both directions during electrophoresis and lie approximately on the diagonal line connecting opposite corners of the gel. Upon reduction, component subunits of proteins connected by interchain disulfide bonds will resolve below the diagonal because the individual subunits migrate faster than the disulfide‐linked complex during the second electrophoresis.