Trypsin was immobilized to poly vinyl alcohol (PVA) by adsorption from its aqueous solutions. The catalytic activity of trypsin increased markedly by irnmobiliZl!-tion for peptide synthesis from N-a-benzoyl L-arginine in hydrophilic organic solvents such as tetrahydrofuran or ethanol. The yield of Bz-Arg-Leu-NH2 is strongly dependent on the PV Ntrypsin ratio and water content in the reaction medium. The optimum pH and temperature were determined for immobilized trypsin as 7.0 and 40°C, respectively