The subunit composition of glutenin was analysed by SDS-polyacrylamide-gel electrophoresis using two varieties of contrasting pedigrees. 'Maris Widgeon', a variety of good bread-making quality, was shown to contain 2 glutenin subunits not present in 'Maris Ranger', a much higher yielding variety that is unsuitable for making bread. A third subunit was only found in 'Maris Ranger' glutenin. To determine if any of these subunits are directly related to bread-making quality, 60 randomly-derived F2 progeny from a 'Maris Widgeon' x 'Maris Ranger' cross were analysed for bread-making quality and for glutenin subunit composition. A strong correlation was demonstrated between the presence of one of the two subunits inherited from 'Maris Widgeon', and quality. This subunit (termed subunit 1 glutenin) had an approx. mol. wt. of 145,000. It was also found in 'Maris Freeman', a bread-making variety selected from the same cross previously made in 1962. In further crosses involving 'Maris Widgeon' or its descendants, more bread-making varieties have been produced in the last decade at the Plant Breeding Institute, Cambridge and all but one have inherited glutenin subunit 1. The subunit has been traced back through 'Holdfast' to 'White Fife', a Canadian hard spring wheat of excellent breadmaking quality. Some 67 varieties were screened for the presence of glutenin subunit 1 and it was found in 31% of them. Several unrelated varieties of good bread-making quality did not contain subunit 1 glutenin.