Technical Abstract: Fructans are thought to have a role in physiological responses and growth under low temperatures in cool season grasses. Two varieties of timothy (Phleum pratense), var Vega, a Scandinavian variety, and var. Climax, introduced from England and currently grown in U.S. were compared to relation to their response to different growth temperatures. Neither of the two varieties accumulated any high DP fructan in leaves when grown at constant day/night temperature of 20 degrees C. At lower temperatures, total carbohydrate levels increased, especially in Vega. At the lowest growth temperatures tested (10/10 degrees C and 10/5 degrees C day/night) a pronounced accumulation of total carbohydrate and high DP fructans occurred. A pronunced accumulation occurred also when plants grown at 20 degrees C were transferred to 10 degrees C for several days before harvest. The change in temperature is thought to induce a temporary imbalance in source and sink activities. The fructans accumulated in the 12-80 DP range. Only very small amounts of small oligosaccharides were detected. The two timothy varieties showed limited qualitative difference in fructan accumulation. Generally Vega had significantly higher total carbohydrate and fructan content than Climax, suggesting possible differences in genetic adaptation to cool growth temperatures.