The synthesis of the dipeptide N-benzoyl-L-tyrosine-L-argininamide (BTAA) was conducted under kinetic control with N-benzoyl-L-tyrosine ethyl ester as acyl donor and argininamide as nucleophile using immobilized alpha-chymottypsin as catalyst. Using a mathematical procedure, the kinetic constants corresponding to the proposed mechanism of peptide synthesis were determined in three different cosolvent media, namely, ethanol, diglyme and acetonitrile. These constants were used for evaluating the selectivity of glyoxyl-agarose immobilized alpha-chymotrypsin in the synthesis of BTAA by determining the ratios of synthesis to hydrolysis rates. (C) 2017, The Society for Biotechnology, Japan. All rights reserved.