The extracted non-denatured cytoplasmic proteins are suitable for many different applications, including Western blotting, immunoassays, protein activity and reporter gene assays. Isolated cytoplasmic proteins can also be used in 1D and 2D electrophoretic analysis. Isolated intact nuclei can either be lysed with the nuclei lysis reagent or stored frozen in the provided nuclei storage buffer for further use. Extracted nuclei can be used for many cell biology applications: isolation of chromatin, histones or nuclear RNA, isolation of total nuclear proteins for use in DNA-protein interaction assays (EMSA), 2D fractionation or other applications. Both, cytoplasmic and nuclear proteins, are compatible with protein quantification assays such as Bradford, Lowry and the BCA assay. The kit provides reagents sufficient for extraction of cytoplasmic and nuclear fractions from 50 samples of 50 µl wet cell pellet or 100 mg of tissue.