This chapter describes a method for the separation of peptides on the cation exchanger Dowex 50, and for the separation on the anion exchanger Dowex 1. The procedure describes the use of Dowex 50-X2, Dowex 50-X8 is also satisfactory with some modification in conditions of development and offer advantages. The chromatographic procedure on Dowex 50 ordinarily yields simpler mixtures that need to be separated further. Although such separation often can be effected by chromatography on Dowex 1, another type of Dowex 50 may also be used. A finely divided, more highly cross-linked cation-exchanger resin equivalent is substituted to Dowex 50-X8 in the procedure. The behavior of peptides is altered by such a substitution, and separations of given peptides take place on one, but not on the other. There are, therefore, some advantages in using a more highly cross-linked resin, and it should perhaps be the resin of choice. The same basic procedures also apply to the use of a more highly cross-linked resin equivalent to Dowex 50-X8. Purification, preparation for column packing, and equilibration are the same as that for Dowex 50-X2.