Theeffect of heat on trypsin inhibitor (TI) activity during steam-infusion cooking of soymilk was studied. At 154°C only 40 s process time reduced TI to the same level as conventional cooking at 99°C for 60 min. Between 99 and 154°C the kinetics of TI inactivation followed behavior exemplified by the summation of two first-order reactions. Spline fitting functions effectively modeled the data with r2 ranging from 0.984 to 0.999. The heat-labile reaction was attributed to Kunitz inhibitor and the heat-stable reaction, to Bowman-Birk inhibitor. The former accounted for approximately 85 percent of the iriginal TI activity. Arrhenius equation kinetic constants for each reaction were calculated.