Publisher Summary This chapter discusses that the gel filtration in its various forms is an efficient tool for the preparations in protein chemistry. It can also be used to test the supposed homogeneity of a protein or peptide preparation. A gel column calibrated with respect to its molecular-sieving properties may also be used to estimate the molecular size of biologically active or otherwise labeled substances before their isolation has been accomplished. It reviews that the result of such estimation must be cautiously interpreted. Dextran gels and other gel substances mentioned can be used as a support in electrophoresis. It should be of great value to find out, if similar separations can be obtained with gel filtration supplemented with “pure” zone electrophoresis as with starch-gel electrophoresis. This survey of the present stage of gel-filtration methods as applied to proteins and peptides has been confined mainly to the dextran gels. It should be realized that the methods outlined should be applicable also to other gels with similar sieving properties.