In acute experiments, the amylolytic, invertase, glycyl-L-tyrosindipeptidase, monoglyceridlipase,and alkaline phosphatase activity of the mucosa homogenate of the rat small intestine was studied 4, 24, 48 and 72 hrs after a two-hour exposure to 36-37 and 40-41 degrees C. No decrease in the activity of any of the ferments was observed. Exposure to heat is concluded to lead to the changes of small intestine ferments spectrum. The character of these changes depends on the heat stress degree and its duration.