Recently, preinduction of the heat shock response has been shown to protect CNS neurons undergoing various stressful insults, e.g., heat, ischemia, or exposure to excitotoxins. However, it is not known which of the proteins induced by the heat shock response mediate the protective effects. Previous correlative evidence points to a role for the highly stress-induced 72-kDa heat shock protein (hsp72). However, it is not known whether hsp72 expression alone can protect against a range of acute neuronal insults. We constructed a herpes simplex virus-1 vector carrying the rat brain stress-inducible hsp72 gene and the Escherichia coli lacZ (marker) gene. Infection with the vector caused hippocampal neurons to coexpress hsp72 and beta-galactosidase. Infection with a control vector led to marker gene expression only. Overexpression of hsp72 protected cultured hippocampal neurons against a heat shock but not against the metabolic toxin 3-nitropropionic acid or the excitotoxin glutamate. This is the first published report of protection following heat shock protein transfection in CNS neurons.