Technical Abstract: This paper describes the isolation of Wheat ABA-responsive mutants (Warm) in Chinese spring background of allohexaploid Triticum aestivum. The plant hormone abscisic acid (ABA) is required for the induction of seed dormancy, the induction of stomatal closure and drought tolerance, and is associated with cold and salt tolerance. ABA also inhibits the germination of mature grain, and higher sensitivity to ABA has been shown to be associated with preharvest sprouting tolerance in wheat. PHS, the germination of seed on the mother plant, occurs when cool moist conditions persist before harvest. PHS tolerance is correlated with higher levels of seed dormancy which can result from red grain color, higher ABA accumulation, or higher levels of ABA sensitivity. The BA sensitivity of wheat grain during germination was found to be associated with the dormancy status of the grain. Warm lines were isolated based on the phenotype of maintaining higher levels of ABA sensitivity during after-ripening. The Warm1 and Warm4 mutants showed increased seed dormancy even in the absence of applied ABA suggesting that these mutants may have increased embryo dormancy. The remaining mutants, Warm2, Warm3, Warm5, and Warm6 all show fairly normal germination in the absence of ABA but increased sensitivity to the inhibition of seed germination by applied ABA. Warm resulted in little or no change in the yield of greenhouse and field grown plants suggesting that they may be utilized to increased grain dormancy without adverse effects on yield. Measurement of whole plant transpiration revealed that Warm3 and Warm6 show a phenotype of decreased leaf transpiration. Since ABA also inhibits leaf transpiration in drying soils, this phenotype suggests that these mutants are likely ABA hypersensitive both in seed and vegetative tissues.