[en] Grain quality in wheat includes hectolitre weight (HLW) besides protein content and thousand-grain weight (TGW). The British winter wheat variety ''Guardian'' has a very high yield potential. Although the long grain of ''Guardian'' results in a desirable high TGW the HLW is too low. To select mutants exhibiting increased HLW the character was first analyzed to identify traits that could more easily be screened for using M₂ seeds. In comparison of 6 wheat cultivars, correlation analyses with HLW resulted in coefficients of -0.86 (grain length, L:P <0.05), +0.45 (grain height, H) and -0.29 (grain width, W). A significant negative correlation (r= -0.85; P <0.05), was observed between HLW and TGW. ''Guardian'' is characterized by highly prolate (i.e. sausage-shaped) grains. It was decided to screen visually a population of approximately 500,000 M₂ seeds for shorter, less prolate grains. Mutagenesis was carried out using EMS sulphonate (1.8 or 3.6%), sodium azide (2 or 20 mM) or X-rays (7.5 or 20 kR). 69 M₂ grains with altered shape were selected. Examination of the M₃ progeny confirmed 6 grain-shape mutants, most of them resulting from EMS treatment (Table). Two of the mutants showed TGW values significantly below the parental variety, but three mutants exhibited HLW and TGW values significantly greater than those of the parental variety. Microplot yield trails on selected M₃ lines are in progress. The influence of physical grain characteristics on HLW offers prospects for mechanical fractionation of large M₂ populations. The application of gravity separators (fractionation on the basis of grain density) and sieves (fractionation on the basis of grain length) in screening mutants possessing improved grain quality is being investigated