Several researchers have postulated that dietary lysine requirements for turkeys are dependent upon ambient temperature. To test and quantify this hypothesis, a factorial experiment was designed with four dietary lysine levels (75, 90, 105, and 120% of NRC lysine recommendations) from 1 d of age onward and two ambient temperatures (15 vs. 30 degrees C) from 4 wk of age onward. Growth performance and carcass yields were measured, and requirements were derived from the fitted exponential response curves at 95% of the maximum possible response above that of the basal diet. In the entire experiment no significant interaction effects between temperature and lysine were observed for feed intake, BW gain, and feed:gain ratio. Exponential curves gave a very good fit (R2 > 0.89) for feed intake, and BW gain responses to dietary lysine concentrations in all age intervals. The dietary lysine requirement was estimated to be 1.67 +/- 0.09%, 1.19 +/- 0.13%, 1.08%, and 0.94 +/- 0.35% from 29 to 56 d, 57 to 84 d, 85 to 114 d, and 115 to 140 d of age, respectively. High temperature decreased all absolute processing yields in kilograms but relative cold carcass yield and relative yields of thighs, drums, and wings were increased by high temperature. Relative breast meat yield and abdominal fat were decreased by high temperature. Turkeys at low temperature responded with more breast meat to high lysine than at high temperature.