Linear gradient gels, which are polyacrylamide gels having a gradient of increasing acrylamide concentration (and linearly decreasing pore size), can have advantages over fixed-concentration SDS-PAGE gels. First, a much greater range of protein M(r) values can be separated on a linear gradient gel than on a fixed-concentration gel. Second, there is a greater likelihood of resolving proteins with very similar M(r) values on gradient gels than on fixed-concentration gels. This protocol describes the pouring of linear gradient gels with a gradient former. The most common gradient gel contains 4%-20% acrylamide; however, the range of acrylamide concentrations should be chosen on the basis of the size of the proteins being separated.