alpha-Amylase from barley malt decayed at a rate of 1.1% h(-1) at 45 degrees C and this decay rate was greatly accelerated at 55 degrees C. Glucose and maltose inhibited the catalytic actions of both bacterial and barley a-amylase in the same manner during the hydrolysis of starch granules. The catalytic activity dropped exponentially as these sugars increased up to 400 g/L; with about 50% activity at 100 g/L. Equations are presented to model both time decay of the enzyme and the inhibition effect of the sugars.