Chinese hamster ovary cells exposed to the sulfhydryl compound cysteamine combined with heat treatment at 44 degrees C developed thermotolerance within 8 h. After initial treatment either with 15 min cysteamine (0.4 mM) at 37 degrees C immediately followed by 15 min heat at 44 degrees C or with 15 min cysteamine (0.4 mM) at 44 degrees C, the magnitude of thermotolerance developed was identical. The D0 of the subsequent 44 degrees C heat survival curves increased by factors of 8.9 and 7.9, respectively. The kinetics of thermotolerance induction and the time to reach the maximum of thermotolerance expression after combined cysteamine treatment at 44 degrees C for 15 min was found to be comparable to the effects of 44 degrees C treatment alone for 30 min. The synergistic effect of cysteamine with the conditioning heat treatment at 44 degrees C was blocked by catalase (50 micrograms/ml). Following initial treatment with cysteamine at 37 degrees C, cells became thermotolerant within 2 h. The D0 of the survival curves for 44 degrees C heat treatments increased with duration (t1 = min, 37 degrees C) of the cysteamine (0.4 mM) exposure; e.g., the D0 increased by factors of 1.5, 1.6, 2.2, and 2.6 for t1 = 30, 60, 90, and 120 min. The induction of thermotolerance by cysteamine at 37 degrees C was completely blocked by the addition of catalase (50 micrograms/ml), present during the initial period of drug treatment. Combined cysteamine and heat treatment at 44 degrees C, but also cysteamine exposure at 37 degrees C, enhanced synthesis of heat shock proteins. The data suggest that oxidative stress by cysteamine can be synergistic with the conditioning heat treatment at 44 degrees C which induces thermotolerance. At 37 degrees C, cysteamine itself induces thermotolerance and the enhanced synthesis of heat shock proteins under these conditions.