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Drought occurring at critical growth and developmental stages in cereals aft'ects productivity by reducing biomass accumulation, grain set. and grain yield and quality. Maize (cv. SR-73). sorghum (cv. Trump), and wheat (cv. Spear) were established in drought-prone field conditions in Perth. Western Australia, in 1994. The plants were then subjected to optimal and suboptimal supplementary watering regimes at growth stages that were sensitive to water availability. Glycinebetaine in aqueous solution was applied to leaves at three rates (2. 4 and 6 kg ha"' and a control) to establish whether its application could ameliorate the effects of drought on the yield of the crops. Abo\eground biomass production was measured at the beginning and at termination of the watering regimes. Leaf tissue glycinebetaine concentrations were determined 1 and 3 weeks after application. At physiological maturity, grains from the crops were harvested and grain yield, number of grains m"-and single grain weight were recorded. Drought significantly reduced abo\e-ground biomass production in mai/e (P ^ 0.047). but not in sorghum and wheat. Grain yield o\' maize, number of grains tn • of maize and sorghum, and single grain weight of sorghum were significantly depressed by drought. Foliar application o\' aqueous glycinebetaine marginally enhanced biomass production in the three crops and significantly increased grain yield of maize (P = 0.001) and sorghum (P = 0.003). It also resulted in more grains m"-of maize, sorghum and wheat (P = 0.001. 0.001 atid 0.003. respectively), with interactions between water and glycinebetaine treatments for sorghum and wheat (P = 0.001 and 0.001. respectively). Residual tissue glycinebetaine levels remained high 3 weeks after application to the crops. The positive eiVects of glycinebetaine treatment appear to be linked to its physiological role as a plant osmoticum that improves drought tolerance. The results of these studies suggest that foliar application of glycinebetaine may be used to improve drought tolerance and economic yield of maize and sorghum, but not of wheat. Increased grain yield was associated with more grains m"' rather than greater single grain weight.