An alternative sieving matrix, replaceable cross-linked polyacrylamide (rCPA), was developed for sodium dodecyl sulfate capillary gel electrophoresis (SDS-CGE) separation of proteins. This rCPA could be conveniently pressurized into separation capillaries under a pressure of 80 psi. SDS-CGE separations using this matrix generated high resolutions for a wide range (approximately 4 kD to approximately 300 kD) of proteins. When compared to the most frequently used sieving matrixes, the rCPA permitted the highest resolutions with comparable or increased separation speed for protein separations.