The ProteoExtract® Transmembrane Protein Extraction Kit (TM-PEK) provides a detergent-free novel chemistry to enable the mild and efficient extraction of transmembrane proteins, such as GPCRs, from mammalian cells and tissues. The fraction enriched in membrane proteins and large protein complexes is directly compatible with enzyme assays, non-denaturing and SDS-based gel electrophoresis, Western blotting and immunoprecipitation. The enriched fraction is appropriate for mass spec-based analysis after a tryptic in-gel digest. The kit contains two different extraction reagents for protein-dependent optimization, protease inhibitor cocktail, and appropriate buffers for processing twenty samples (2-5 x 106 cells or 25-50 mg tissue per sample).