Summer dormancy level becomes more critical for tall fescue persistence under high summer temperatures. A growth chamber study was conducted to examine the summer dormancy level x soil moisture x temperature interaction. Seed of Jesup (summer active), AGRFA 125 (highly summer dormant), and Flecha (obligatory summer dormant), all infected with AGRFA 125 endophyte, were planted in 15 cm pots and placed in the greenhouse. In early May, the soil water capacity (SWC) was gradually reduced from 90% to 15% to simulate a 6 week drying down period to induce summer dormancy. After defoliating to a 5 cm height, 9 plants of each entry were placed in each of four growth chambers. In each growth chamber, 3 plants of each entry were maintained at 15, 45, or 90% SWC for 6 weeks. Two of the chambers were set at night/day temperatures of 25/35°C and two at 15/25°C with a 15 hour day length. After 6 weeks the high temperature growth chambers were changed to the low temperature and plants watered to 90% SWC to determine plant survival. At the low temperature treatment all plants survived with shoot yield increasing with increasing SWC and decreasing summer dormancy. In the high temperature treatment there was no growth at 15% SWC with limited growth at the 45 and 90% SWC levels. Plant survival at the 15% SWC was 67, 0, and 17% for Flecha, AGRFA125, and Jesup respectively. Survival at the 45 and 90% SWC ranged from 67 to 100% with little difference among entries. The high temperature treatment of 250C nights and 350C days limited growth of all entries and reduced plant survival at low moisture levels except for the obligatory summer dormant Flecha.