INTRODUCTIONThe ammoniacal silver staining method is one of the most sensitive methods used to detect proteins on an SDS-PAGE gel. However, this and other standard silver staining methods are not compatible with mass spectrometry (MS), which is fast becoming the best way to identify proteins isolated on 2D gels. Because the proteins in gels to be analyzed by mass spectroscopy cannot be modified, many of the common sensitizing agents (e.g., glutaraldehyde and strong oxidizing agents) cannot be used. This method is compatible with MALDI and ESI-MS, and it shows an increased ability to deal with semipreparative protein loads without negative staining as compared with other silver staining methods. However, this process is less sensitive than standard silver staining methods.