INTRODUCTIONFollowing the separation of proteins by IEF, the second dimension is carried out by SDS-PAGE. This protocol details the method for casting single homogeneous SDS-PAGE gels. Homogeneous gels (with the same %T and %C throughout) offer the best resolution for a particular molecular-weight range and are commonly used because they are the easiest to pour reproducibly. The second-dimension gels can be conveniently prepared in three different formats (i.e., sizes): minigels, for use with 7-cm IEF first-dimension gels; standard gels, for use with 11-, 13-, and 18-cm IEF first-dimension gels; and large-format gels, for use with 18- and 24-cm IEF first-dimension gels. All of the gels use a common set of reagents, listed below, but differ slightly in the equipment required.