The high molecular weight (HMW) constituents of beer comprise carbohydrate, tannin, and protein complexes. Evidence is accumulating that these components form a dynamic, interacting system contributing to the head retention and the stability properties of beer. Various procedures for isolating individual fractions have been developed. These have included ammonium sulphate or ethanol precipitation; chromatography on ion-exchange resins, silica gel, and other adsorbing materials; electrophoresis; and gel filtration. In each case, the fractions isolated have consisted of groups of molecules either chemically associated, or having roughly similar physico-chemical properties. A powerful new technique that of immunoelectrophoresis, has been applied to beer by several workers. It has given results suggesting that some barley proteins may be carried through the malting and brewing processes without change in their antigenic properties. A system of references of barley proteins based on this technique has recently been developed by the European Brewery Convention.