The dynamics of thermotolerance in wheat seedlings (Triticum aestivum L.) of cv. Moscovskaya 39 depending on the intensity of high temperature impact was studied. The temperature ranged from 33 to 45 °C with an interval of 2°. The temperatures 33, 35, 37 and 39 °С had essentially the same effect on the seedlings: thermotolerance rose to a maximum and then remained unchanged. Thermotolerance at these temperatures differed only in a quantitative sense. When the temperature was raised to 43–45 °С, the pattern of change in thermotolerance of seedlings was qualitatively different. In this case, at 43 °С, as well as at 45 °С, thermotolerance first grew rapidly but then dropped sharply. The temperature of 41 °C appeared to be an interstage between 33–39 °С and 43–45 °С. The data obtained suggest that the pattern of plant response to the high temperature impact can vary not only quantitatively but also qualitatively, depending on the intensity of the impact.