ABSTRACT The effect of different combinations of temperatures and exposure times on the mortality of Heterodera schachtii eggs was assessed in two different experiments under laboratory conditions. In the first experiment, cysts in water were exposed to 25, 35, 37.5, 40, 42.5, 45, 47.5, 50, or 52.5 degrees C for a maximum period of 2 h. In the second experiment, cysts in naturally infested soil were exposed to 25, 32.5, 35, 37.5, 40, 42.5, or 45 degrees C for a minimum period of 2 h to a maximum of 2,048 h. Viability of eggs in cysts was assessed by a hatching test in 3 mM zinc chloride solution. Viability in water was suppressed after 2-h exposure at 50 degrees C and inhibited after 1 to 2 h at 52.5 degrees C. Emergence of juveniles from cysts in soil was greater at the lower temperature x exposure time combinations and suppressed at higher combinations. Egg mortality started after exposure for 256 h at 40 degrees C, 32 h at 42.5 degrees C, and 16 h at 45 degrees C, and 81, 31, and 7 h of exposure were necessary to kill 50% of the nematode egg population at 40, 42.5, and 45 degrees C, respectively. The data fitted the models P(t) = P(0)10(-t/ (q + mT)) and P(T1) = P(T0)10(-T/(z - pt)) for m = -0.0111, q = 0.8238, z = 2.444, and p = -0.23.