Chinese hamster ovary (CHO) cells were treated with the thiol oxidant diamide for 1 hr at 37 degrees, incubated in diamide-free medium for 4 hr at 37 degrees, and then exposed to hyperthermic treatment (43 degrees) or assayed for the presence of 110, 90 and 66 kilodalton (kD) stress (heat shock) proteins. Cellular inactivation produced by the hyperthermic treatment was measured using colony formation as the end point. Low concentrations of diamide, which did not result in depletion of intracellular GSH, induced a moderate degree of protection against thermal toxicity but did not affect the pattern of protein synthesis. Exposure to 0.4 mM diamide, which reduced intracellular GSH concentrations by 50-60%, significantly reduced the rate of hyperthermic cellular inactivation. This occurred coincidentally with the synthesis of stress proteins of approximate molecular weights of 110, 90 and 66 kD. Furthermore, this concentration of diamide protected cells from thermal inhibition of protein synthesis. These results indicate that thiol oxidation by diamide can induce both the development of thermal resistance to cellular inactivation and the synthesis of stress proteins.