Wheat grain protein composition depends both on genotype and environment factors which influence the rate and duration of wheat grain development and protein accumulation. The objective of this study was to investigate the impact of drought stress and N fertilization on plant N partitioning, grain protein content, and grain protein composition of nine white winter wheat cultivars. Varieties were grown at two Oregon locations in 2003 and 2004 under line-source irrigation systems with two levels of soil nitrogen. Irrigation treatments were applied during grain fill to achieve three moisture levels, representing 100, 80, and 50 % of optimum. Plants were sampled early and late during the grain filling period to determine N content of stems, leaves, and heads. Glutenin, gliadin, and non-gluten fractions of flour protein were analyzed by size-exclusion HPLC. Total leaf biomass and leaf N content at both the early and late stages of grain fill were positively correlated with grain protein content. Water stress and N fertilization both had an influence on grain protein concentration. However, the treatments had no clear effect on N partitioning in the plant. As expected, grain protein content was negatively related with both yield and kernel size. Amounts of gliadin and glutenin proteins increased in response to increasing total grain protein. Moisture stress resulted in increased glutenin concentration at both N levels and for all HWW and SWW cultivars. The relative proportion of gliadin proteins increased with increasing grain protein content, regardless of whether increased protein was related to N or water stress. Management strategies to achieve higher grain protein content will be important to production of hard white wheat in the Pacific Northwest. This study suggests that, with increased protein content resulting from either soil N or water stress, changes in protein composition and end-use quality will be relatively similar.