Dry-heat treatment of a dialyzed whey protein isolate at 80°C for 7 days resulted in a decrease in hardness (from 1.55N to 0.49N) of gels formed from a 12% solution. Partial denaturation and progressive polymerization of protein was observed. The monomeric β-lactoglobulin concentration of the whey decreased from 60.64% to 33.33%after 7 days at 80°C. The rate constants determined at 40 to 80°C were used to calculate an Arrhenius relationship for the polymerization. After one year at 25oC, 18% of monomeric β-lactoglobulin was projected to be converted to higher-molecular-weight material. The polymerization apparently did not involve disulfide cross-links.