Proteomics offers unique possibilities to investigate changes in the levels and modifications of proteins involved in the pathomechanisms of diseases and toxic events. However, search for potential drug targets and disease or toxicity markers is limited by the fact that mainly the high-abundance, hydrophilic proteins are visualized in two-dimensional gels. Here we studied the enrichment of rat liver cytosolic proteins by preparative electrophoresis. Preparative electrophoresis was performed with the PrepCell apparatus in the presence of 0.1% lithium dodecyl sulfate. Lithium dodecyl sulfate was exchanged against agents compatible with isoelectric focusing prior to the two-dimensional gel electrophoresis. Proteins were identified from two-dimensional gels by matrix-assisted laser desorption ionization time-of-flight mass specrometry. Low- and middle-size proteins and low-abundance proteins, which had not been found before, were enriched by preparative electrophoresis. The present study represents a contribution of proteomics in the quantification of differences in the levels of low-abundance liver proteins in toxicity studies.