Ion exchange HPLC is a very useful but underutilized tool for peptide purification. Ion exchangers provide separations that are complementary to reversed-phase HPLC. Purification procedures utilizing both ion exchange and reversed-phase modes have greatly increased resolving power compared to procedures that use reversed-phase alone. This increased resolution is particularly useful for the purification of natural peptides from complex tissue extracts and for synthetic peptides from the many structurally similar byproducts of synthesis and HF cleavage. The high capacity of ion-exchange HPLC columns allows them to be used at the front end of a purification scheme, reducing the sample load on subsequent reversed-phase columns. In addition to improving overall resolution in a purification scheme, the charge selectivity of ion exchangers solves specific resolution problems involving charge differences between peptides.