In order to investigate the effects of elevated temperatures during grain development on seed quality, a series of experiments was carried out under both controlled environment and glasshouse conditions. Plants of several cultivars of barley (Hordeum vulgare L.) were subjected to different temperature regimes (18^oC, 30-18^oC, 30^oC and 18-38^oC) during grain development and, after harvest, the seeds were tested for vigour. Grains which had experienced elevated temperatures for part or all their developmental period were lighter and had smaller embryos than grains which experienced 18^oC for most or all of their developmental period. There was a significant positive correlation between grain dry weight, and embryo dry weight. When eleven genotypes were grown in a glasshouse at approximately 18^oC/13^oC (day/night) and a day length of 18 h, grain dry weight and embryo dry weight varied according to genotype. Genotypes with heavier grains had larger embryos than those with lighter grains. Germination tests were carried out using 5ml of distilled water per 100 grains. The germination of grains grown in all temperature regimes was > 94%. Grains which had experienced elevated temperatures during grain development had a higher percentage germination in tests using 8 ml and 10 ml of water per 100 grains than grains which had experienced 18^oC throughout grain development. Seedlings from grains grown in elevated temperatures had fewer roots and had seminal roots which were shorter than those of seedlings from grains which had experienced low temperature throughout development. It was found that plumule lengths were either similar in all seed lots, or that seedlings from grains grown at elevated temperatures had longer plumules than those from grains grown at 18^oC. When seeds were planted at depth of 4 cm in fine sand in pots, seedlings from grains grown at elevated temperatures emerged earlier than those from grains grown at 18^oC.