The effect of different intensities of water stress imposed during the first three weeks of grain filling were determined on the protein content, protein composition and bread volume of three spring wheat cultivars. Water stress was induced by watering the plants with a nutrient solution containing 0%, 15% and 22.5% polyethylene glycol (PEG 6000). Water stress generally decreased the protein content and bread volume by decreasing the production of the reserve proteins, gliadin and glutenin. The lower PEG-concentration had a more pronounced effect than the higher concentration, because the effect of the higher concentration on the production of protein, relative to non-protein components, was less than that of the lower PEG concentration. In this study cultivars did not differ in their response to different intensities of water stress.