In Canada in 1993, a special market class of wheat, Canada Western Extra Strong (CWES), was established to segregate wheat varieties known to produce very strong and extensible doughs. These exceptional dough properties enable CWES cultivars to be blended with wheats of lesser quality as well as being suited to the manufacture of frozen dough products. The high molecular weight (HMW) glutenin allele (Glu-B1al) that confers these properties, particularly dough strength, has now been identified. Typically, the presence of the Glu-B1al (7+8*) allele is associated with the overexpression of HMW-GS 1Bx 7. RP-HPLC was used to quantify the proportion (% area) of individual HMW-GS relative to total HMW-GS in wheat varieties of different origin. The B genome contributed the highest percentage of HMW-GS, with the exception of Glu-B1d (6+8*) where the D genome contributed the most. Cultivars that possessed the Glu-B1al allele contained a significantly higher (P < 0.001) proportion of HMW-GS (56.80 ± 3.25%) encoded by the B genome. This suggests that the proportion of Glu-B1 subunits, relative to the total amount of HMW-GS expressed, has a major effect on dough strength. We also identified germplasm, of different origin, that contains the Glu-B1al allele and overexpresses subunit 7, including the most likely source of this allele in bread wheat cultivars. The Glu-B1al allele in the varieties identified in this paper could be traced, at least through one parent, to the Argentinean bread wheat cultivar Klein Universal II. RP-HPLC elution and expression profiles of various common HMW-GS are also discussed.