Although experience with watersoluble, globular proteins supports Stokes radius as an appropriate size parameter, governing elution position, for both classical and HPLC gel columns, extrapolation of this concept to other kinds of conformation and substances requires caution. Current evidence suggests the viscosity based Stokes radius as the best suited size parameter for many flexible macromolecules (guanidinium HCl denatured proteins, dextrans), whereas many detergent micelles and detergent solubilized membrane proteins elute somewhat earlier, and elongated (e.g. myosin) or SDS denatured proteins elute later, than indicated by their hydrodynamic behaviour. The review includes a discussion of the use of globular proteins of known size to characterize gel pore size distribution.The purpose of this review is to briefly consider the scope of gel chromatography, or size exclusion chromatography (SEC), in the determination of sizes and molecular masses of proteins. This kind of separation is performed either as classical type chromatography, using gels such as Sepharose (agarose), Sephacryl (allyl-dextran crosslinked with Ν,Ν-methylene bisacrylamide) and Superose, or by HPLC with the aid of matrices capable of withstanding high pressures such as silica based TSK SW-or polyacrylamide based TSK PW columns. We first briefly review the theoretical foundation for use of the technique in the estimation of molecular mass and size of watersoluble, globular proteins. We then proceed to consider the use of the technique to analyze other kinds of proteins (elongated or fibrous type proteins, detergent-solubilized membrane proteins) and the effect of a disordered conformation (SDS-or GuHCl denaturation). Finally, we consider the use of globular proteins in the characterization of the pore characteristics of the gels.