We recently demonstrated that heat treatments, capable of triggering thermotolerance development in MH-7777 cells, also induce a transiently increased synthesis of a small set of polypeptides, a phenomenon similar to the heat-shock-protein (HSP) induction demonstrated in various organisms. A close temporal relationship was also found between HSP synthesis and thermotolerance development, and the degradation kinetics of the newly synthesized HSPs very closely paralleled the decay of the thermotolerant state. In the present study, we extended our analysis to determine whether various experimental conditions known to affect thermotolerance development (duration and temperature of the conditioning treatment, step-down heating, ethanol exposure) will also influence HSP synthesis and, conversely, whether agents known to induce (sodium arsenite) or to impair (cycloheximide) HSP production will similarly affect thermotolerance. The results suggested that the expression of HSP and thermotolerance in MH-7777 cells are most likely regulated by some interrelated mechanisms, but indicated that HSP synthesis is neither a sufficient or necessary condition for thermotolerance development.