The electrophoresis of hydrophobic proteins underwent significant development during the last decade. In native gel electrophoresis, the induced charge shift, the involvement of mild detergents as well as a constant ionic strength in the electrophoresis, overcame the difficulty of the low solubility and aggregation of the hydrophobic proteins, and critically improved the results of their native PAGE (H. Schagger, G. von Jagow, Anal. Biochem. 166 (1987) 368). In isoelectric focusing electrophoresis, the most difficult one for hydrophobic proteins, the including of mild detergents, the use of diluted samples with immobilized pH gradient, as well as a more hydrophobic media such as polyethylene glycol methacrylate- acrylamide copolymer improved the resolution and yield of these proteins (J. Schupbach, R.W. Ammann, A.U. Freiburghaus. Anal. Biochem. 196 (1991) 337). In SDS PAGE, contradicting the general belief that it is denaturing, a new development in this technique may permit the complete removal and exchange of SDS bound to proteins and restoration of the latters' activity (M. Dong, L.G. Bagget, P. Felson, M. LeMaire, F. Pennin, Anal. Biochem. 247 (1997) 333). With the use of mild detergents and charge shift of the proteins, native electrophoresis resolving proteins while maintaining activities is now possible. Preparation of active membrane proteins with electrophoresis principles can thus be realized and improved by some new technique such as ''Free-flow electrophoresis''. Membrane protein preparation will be more and more sophisticated, contributing to the characterization, crystallization and structure determination of these biologically important macromolecules. # 1999 Elsevier Science B.V. All rights reserved.