Whey proteins are well known for their high nutritional quality and versatile functional properties. [beta]-Lactoglobulin and [alpha]-lactalbumin are known to interact with each other and form complexes when exposed to heating temperatures above their denaturation temperature. The purpose of this research was to investigate the interactions between the two major whey proteins, [beta]-lactoglobulin and [alpha]-lactalbumin, at the onset of denaturation, and to attempt to foster a better understanding of the mechanism of the formation of heat-induced aggregates and gels. Interactions between whey proteins in mixed systems were studied using gel filtration chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The effects of protein composition, heating temperature, and heating time on the interactions between the two major whey proteins at pH 7.0 were studied. The quantity and size of aggregates (aggregates of large molecular weight >300 kDa and intermediate molecular weights >100 kDa) formed was significantly affected by protein composition and temperature. The aggregates formed were found to be mainly comprised of [beta]-lactoglobulin, whereas, the intermediate aggregates were predominantly comprised of [alpha]-lactalbumin.