OBJECTIVE Possible mechanisms that promote or interfere with the effects of laser ablation of the liver have not been clarified. The aim of this study was to define the chronological alterations in the normal rabbit liver at early stages after laser ablation. METHODS Rabbit livers were ablated with a laser via an optical fiber and then analyzed histopathologically by immunostaining for heat shock protein 70 (HSP70) and by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) method. RESULTS The lesions increased in size progressively over the 24 h that followed ablation and the area of the lesion coincided with the area that had been heated above 43 degrees C. TUNEL-positive hepatocytes were surrounded, at some distance, by HSP70-positive hepatocytes were surrounded, at some distance, by HSP70-positive hepatocytes at 6 h, and such cells were in contact with each other at 24 h. CONCLUSIONS Injury to hepatocytes induced by laser ablation increases for 24 h and dying cells express nuclear HSP70, with subsequent fragmentation of DNA.