Heat shock response and programmed cell death are cellular reactions to stressful stimuli. Previous studies have not correlated these responses in vivo at the spatial level in mammalian tissues. This study uses a dual procedure involving immunocytochemistry for Hsp70 localization and the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end–labeling (TUNEL) assay for cell death to correlate the pattern of stress-inducible Hsp70 and cell death at the cellular level. After whole-body hyperthermia in the rat, an increase in Hsp70-positive cells and TUNEL-positive cells was noted in brain, thymus, and bone marrow. However, 2 populations of cells were apparent in the tissues examined, those inducing Hsp70 and those triggered into programmed cell death. Cells that were both Hsp70 positive and TUNEL positive were rarely detected. In tissues of the intact mammal, cells that induce Hsp70 after whole-body hyperthermia were not triggered into programmed cell death.