Heat-shock protein 70 (HSP70) is expressed in response to various stressful stimuli, and generally used as a histological marker of cell damage. While paraquat has previously been shown to cause HSP70 expression as a result of the oxidative cell damage, recent study has shown that HSP70 expression induced by paraquat poisoning is no longer observed at 18hr after the drug administration in the senescence-accelerated mouse liver, thereby raising the question whether the cell damage is always accompanied by elevated HSP70 expression. To affirm the relevance of HSP70 expression as a marker of the cell damage, the expression of HSP70 immunoreactivity and lipid peroxidation in paraquatpoisoned rat liver were examined. The immunostaining of HSP70 was still clearly detected at 24hr after the drug administration. Lipid peroxidation, a biochemical maker of the oxidative cell damage, was also elevated by the same treatment, suggesting that the expression of HSP70 immunoreactivity observed here may reflect the oxidative-damage to liver cells. These results seem to provide evidence supporting the relevance of HSP70 expression as a histological marker of paraquat-induceddamage to rat liver cells.