Bovineb-lactoglobulin was hydrolyzed with trypsin or chymotrypsin in the course of heat treatment at 55, 60 and 65°C at neutral pH. At these temperaturesb-lactoglobulin undergoes signi®cant but reversible structural changes. In the conditions used in the present study,b-lactoglobulinwas virtually insensitive to proteolysis by either enzyme at room temperature, but underwent extensive proteolysis when either proteasewas present during the heat treatment.