Chromatography of commercial rennet was studied on biospecific sorbents obtained by means of coupling of activated Sepharose 4B with epsilon-aminocapronyl-D-phenylalanine methyl ester and amide, epsilon-aminocapronyl-L-phenylalanyl-D-phenylalanine methyl ester, gramicidin S and N-2,4-dinitrophenylhexamethylenediamine. A mixture of two similar on their specificity enzymes chymosin and bovine pepsin was isolated from rennet by the chromatography on these sorbents. The individual enzymes might be isolated by chromatography on immobilized ribonuclease at pH 3,0, or by means of electrofocusing in pH gradient 4-6. Coloured inhibitor of acid proteases, N-diazoacetyl-N'-2,4-dinitrophenyl-ethylenediamine (DDE) is found to inactivate chymosin at pH 5,6 in the presence of Cu2+,one residue of the inhibitor being attached to the enzyme molecule. Unlike pig pepsin, chymosin is not inhibited with DDE at pH 4,7 and at the enzyme:DDE:Cu2+ ratio being 1:40:40. a synthesis of peptide sorbents is described.