The proteolytic activity of soluble trypsin was studied after the effect of different freezing-thawing conditions ranging from 0 to 196 degrees C. The enzyme is inactivated most essentially during a slow warming of the preparations under experiment. The trypsin activity decrease is found to depend directly on the number of the freezing-thawing cycles. The loss of the enzymic activity within 3h after the effect of low temperatures and warming is irreversible. The data obtained give reason to consider the leading role of the physicochemical factors arising at the stage of the enzymic preparations thawing in the mechanism of trypsin cryodestruction.