The quality of wheat-based foods and the processing properties of wheat flour dough are strongly related to the presence and properties of very large glutenin protein aggregates. These very large aggregates are insoluble in 1.5% (w/v) SDS and can be recovered after ultracentrifugation as a gel, the so-called Glutenin Macro Polymer (GMP) fraction. GMP quantity and gel properties strongly correlate with flour technological quality, but details on factors governing GMP quantity and properties is still missing. We therefore studied factors governing GMP formation. Flour from four wheat varieties: Galahad-7, Caprimus, Soissons and Classic were used in this study. GMP was isolated from each of the flour samples and characterised. Plateau values of G′ paralleled differences in wheat quality. Further detail was obtained by studying dispersions of GMP in 1.5% SDS. Re-aggregation, viscometry and Confocal Scanning Laser Microscopy confirmed that GMP consists of very large particles, able to form a gel. Clear differences in average particle size and re-aggregation (gel-forming) properties could be measured. The size and shape of the particles point to a possible origin from the protein bodies in immature wheat endosperm. © 2003 Elsevier Science Ltd. All rights reserved.