A substrate of diamine oxidase hexamethylene diamine was covalently bound through adipinic acid dihydrazide to Sepharose 4B in order to prepare a sorbent for the purification of diamine oxidase by means of biospecific (affinity) chromatography. A method was developed to purify diamine oxidase from pig kidney cortex using the sorbent. The method, comprising three steps, yielded enzyme preparations with specific activity 2 000-fold higher than that of kidney homogenate.