A novel method for the use of CM-Sephadex in affinity chromatography is described. This method involves a carbodiimide-mediated synthesis of a lactone derivative, which is subsequently hydrazinolyzed to CM-Sephadex hydrazide. More than 90% of the carboxyl groups was converted to the hydrazide form by this method without any discernible degradation of the Sephadex beads. The hydrazide beads were further converted to the axide form and coupled with D-arginine and D-phenylalanine derivatives. These Sephadex derivatives contained more than 0.5 mmol of each amino acid per g dry beads and were found to be effective and specific adsorbents for carboxypeptidase B. This CM-Sephadex hydrazide should be useful in affinity chromatography because the resulting specific adsorbents involve stable amide coupling linkages and retain the physical properties of their precursor, Sephadex, which are favorable for column operation.