Heat-shock proteins DnaK, DnaJ, and GrpE (KJE) from Escherichia coli constitute a three-component chaperone system that prevents aggregation of denatured proteins and assists the refolding of proteins in an ATP-dependent manner. We found that the rate of KJE-mediated refolding of heat- and chemically denatured proteins is decreased at high temperatures. The efficiency and reversibility of protein-folding arrest during and after heat shock depended on the stability of the complex between KJE and the denatured proteins. Whereas a thermostable protein was released and partially refolded during heat shock, a thermolabile protein remained bound to the chaperone. The apparent affinity of GrpE and DnaJ for DnaK was decreased at high temperatures, thereby decreasing futile consumption of ATP during folding arrest. The coupling of ATP hydrolysis and protein folding was restored after the stress. This strongly indicates that KJE chaperones are heat-regulated heat-shock proteins which can specifically arrest the folding of aggregation-prone proteins during stress and preferentially resume refolding under conditions that allow individual proteins to reach and maintain a stable native conformation.