The distribution of the 72-kDa heat-shock protein (hsp72) in rat brain, 24 h following in vivo transient hyperthermia (41.5 degrees C, 15 min), was studied using immunohistochemistry (n = 22). Tissue sections were also stained with hematoxylin and eosin, and with an anti-glial fibrillary acidic protein to evaluate neuronal and astrocytic response to transient hyperthermia, respectively. hsp72 was observed in glia and endothelial cells throughout brain. hsp72 was also found in neurons located in the: dentate gyrus, habenula, and hypothalamus, granular layer of the cerebellum and the olfactory area. Our data indicate, that hyperthermia causes neuronal expression of hsp72, particularly in cerebral neuronal populations which control the neuroendocrine stress response.