A gel protein capillary extraction apparatus is developed and demonstrated for its rapid and effective transfer of SDS-protein complexes from polyacrylamide gel to a fused-silica capillary. The small dimensions of capillary columns permit the application of high voltages for achieving rapid and effective transfer of gel proteins. Furthermore, the fused-silica capillaries are internally coated with polyacrylamide for the elimination of electroosmotic pumping and protein adsorption onto the capillary wall. The extracted proteins are present in a highly concentrated solution plug as the result of field amplification and sample stacking during the extraction process. Three model proteins, including cytochrome c (14 kDa), ovalbumin (45 kDa), and beta-galactosidase (116 kDa), are visualized using coomassie blue staining and electrophoretically extracted from the gels with protein loading as low as 50 ng. The SDS-cytochrome c complexes extracted from a 50-ng protein loading are concentrated in a 30-nL solution plug inside the capillary with an estimated concentration of 0. 1 mg/mL or 10(-5) M. The capillary format allows the straightforward integration of a miniaturized trypsin-membrane reactor for on-line proteolytic digestion and ESI-MS analysis for protein/peptide identification.