Heat shock (44 degrees C for 10 min) or ATP depletion by an uncoupler (CCCP for 20 min) is shown to result in stimulation of hsp68/70 synthesis in Ehrlich tumor cells. After 3 h of recovery, the cells become thermotolerant. Surprisingly, repeated ATP depletion caused by CCCP or rotenone (a respiratory inhibitor) treatment, had a much lower effect on cell viability. Both induction of tolerance to energy deprivation and hsp68/70 synthesis were totally suppressed by cycloheximide, an inhibitor of cytosolic protein synthesis. In tolerant cells, rotenone still induced ATP depletion; however, protein aggregation (the rise in Triton-insoluble proteins) was inhibited in these cells. It is suggested that cellular chaperones (e.g. hsp70) are involved in the protection of ischemic cells from necrosis, preventing protein aggregation under ATP deficiency.