Yield and developmental characteristics of crop genotypes grown at different levels of water availability are often used to select genotypes that are adapted to variable moisture environments. Field studies were conducted at Aberdeen, Idaho, USA in 1992 and 1993 to evaluate the effects of varying moisture supply on grain yield and yield components of spring wheat genotypes. In both years, 12 spring wheat (Triticum acstivum L.) genotypes were grown under three irrigation levels (well-watered, moderate water-stress and severe water-stress) imposed during the periods from mid-tillering to anthesis with a line source sprinkler irrigation system. Grain yield and yield components (spikes m-2, spikelets spike-1, kernels spikelet-1, kernels spike-1 and kernel weight) were used to evaluate the genotypic response to water stress. Overall, water stress caused a reduction in grain yield and yield components. Genotypes exhibited a large year-to-year variation in their ranks for grain yield. Medium-tall growing genotypes (IDO 367, IDO 369 and Rick) generally produced high yields under water stress conditions in 1992 (relatively dry year), while short -medium genotypes (WPB 926. Yecora Rejo and Pondera) produced high yields under water stress conditions in 1993 (relatively wet year). Chris and Serra were the lowest yielding genotypes under water stress conditions in both years Under moderate stress conditions, IDO 367 and Yecora Rojo had consistently high yields. Genotypie yield differences under water stress conditions were primarily related to the differences in the numbers of spikes m-2. Therefore, a tendency for spikes per unit area could be used to select wheat genotypes for improved drought tolerance high plasticity.