High pressure treatment of solutions of beta-lactoglobulin (beta-Lg) or beta-casein (beta-Cn) in the presence of microbial transglutaminase for 90 min at 40 degreesC resulted in an enzyme-induced oligomerization of the proteins at a pressure of 400 MPa. After analogous high-pressure treatment of a solution containing beta-Lg and beta-Cn, the formation of dimers and trimers consisting of beta-Cn crosslinked with beta-Lg was demonstrated by SDS-PAGE and immunoblotting for the first time. The formation of such heterologous oligomers offers the possibility of directly affecting the functional properties of the proteins and reveals new technological possibilities in food production.