Mohammed, A. R. and Tarpley, L. 2011. High night temperature and plant growth regulator effects on spikelet sterility, grain characteristics and yield of rice (Oryza sativaL.) plants. Can. J. Plant Sci. 91: 283-291. The presence of seasonally high night temperature (HNT) as a result of global warming, occurring during the critical stages of development, could reduce rice yield and quality. To understand how a combination of HNT and plant growth regulators (PGR; a-tocopherol and glycine betaine) affects yield and yield-related parameters of rice plants, we conducted three pot experiments under two levels of night temperature (NT; 27 and 32^oC) with or without PGR treatments. Plants were subjected to a HNT through the use of continuously controlled infrared heaters, starting 20 d after emergence (DAE), from 2000 until 0600. Plants were treated with a-tocopherol and glycine betaine 20 DAE. The NT had no effect on number of productive tillers, main-stem panicle length or number of primary branches per panicle; however, reduced yield resulted from significant effects on spikelet sterility (SS), and grain length, width, and weight. The grains located at the base of the panicle showed decreased length and width compared with grains located at the tip of the panicle. Application of glycine betaine increased grain yield by predominantly decreasing SS in rice plants, suggesting the potential future use of glycine betaine to help partially prevent HNT damage to rice.