Wheat (Triticum aestivum L.) cultivars grown in the southern Great Plains of the U .S .A. are exposed to a wide range of moisture conditions due to large fluctuations in the amount and frequency of rainfall . Yield stability under those conditions is therefore a desirable trait for wheat breeders . Our primary objective was to quantify various genetic parameters for grain production in drought-stressed and irrigated environments . We also attempted to predict and measure yield responses when selection is practiced in either droughtstressed or irrigated environments, or both . Seventy F2-derived lines from the cross, TAM W-101/Sturdy, were evaluated at Goodwell, OK, under irrigated and naturally drought-stressed conditions in 1987 and 1988 . Genetic variance and heritability estimates were higher in the irrigated environment than in the drought-stressed environment . The genetic correlation coefficient for yields in the two environments was 0.20 Β± 0 .16, indicating that selection of widely adapted genotypes requires testing in both environments . Based on the genetic variance/covariance structure of this particular population, the linear index which maximized the combined expected gain in both environments was 0 .66Y, + 0 .34Y2, in which Y, and Y2 are yields in the irrigated and drought-stressed environments . This index is not expected to apply across all populations ; rather, it further supports the hypothesis that testing in either environment alone (drought stressed or irrigated) may not be most effective for increasing either mean productivity or yield under drought stress.