Due to their heterogeneity and huge differences in abundance, the detection and identification of all proteins expressed in eukaryotic cells and tissues is a major challenge in proteome analysis. Currently the most promising approaches are sample prefractionation procedures prior to narrow pH range two-dimensional gel electrophoresis (IPG-Dalt) to reduce the complexity of the sample and to enrich for low abundance proteins. We recently developed a simple, cheap and rapid sample prefractionation procedure based on flat-bed isoelectric focusing (IEF) in granulated gels. Complex sample mixtures are prefractionated in Sephadex gels containing urea, zwitterionic detergents, dithiothreitol and carrier ampholytes. After IEF, up to ten gel fractions alongside the pH gradient are removed with a spatula and directly applied onto the surface of the corresponding narrow pH range immobilized pH gradient (IPG) strips as first dimension of two-dimensional (2-D) gel electrophoresis. The major advantages of this technology are the highly efficient electrophoretic transfer of the prefractionated proteins from the Sephadex IEF fraction into the IPG strip without any sample dilution, and the full compatibility with subsequent IPG-IEF, since the prefactionated samples are not eluted, concentrated or desalted, nor does the amount of the carrier ampholytes in the Sephadex fraction interfere with subsequent IPG-IEF. Prefractionation allows loading of higher protein amounts within the separation range applied to 2-D gels and facilitates the detection of less abundant proteins. Also, this system is highly flexibile, since it allows small scale and large scale runs, and separation of different samples at the same time. In the current study, this technology has been successfully applied for prefractionation of mouse liver proteins prior to narrow pH range IPG-Dalt.