Abstract The trypsin-catalyzed hydrolysis of benzoyl- l-arginine ethyl ester (BAEE) has been studied systematically at pH 7.8 and 32°C with a nonlinear regression model. The Michaelis constants covering the range from pH 7.0 to 8.6 were determined. The concentrations of enzyme isolated from pig pancreas were determined using the SAW-impedance sensor and the spectrophotometry, respectively. The experimental detection limit of trypsin was 0.3 mU/ml 2 2 mU/ml expresses milliunits per milliliter. One unit of enzyme is defined as the amount of trypsin required to hydrolyze 1 μmol of substrate per minute at 32°C and pH 7.8. and the recovery of the sensor system ranged from 94.7 to 105% ( n= 6). The effects of temperature, pH, and some metal ions on the trypsin activity were investigated.