GST-tagged proteins can be purified directly from pretreated bacterial lysates using GSTrap 4B. GST-tagged proteins are eluted under mild, nondenaturing conditions using reduced glutathione. The purification process preserves protein antigenicity and function. If desired, cleavage of the protein from GST can be achieved using a site-specific protease whose recognition sequence is located immediately upstream from the multiple cloning site on the pGEX plasmids. GST-tagged proteins can be detected using colorimetric or immunological methods. The resin, Glutathione Sepharose 4B, is also available as lab packages and is a good choice for scale-up. The columns can be operated with a syringe, peristaltic pump, or liquid chromatography system such as ÄKTA design or FPLC System.