The well-known difference in sensitivity of mice and rats to acetaminophen (APAP) liver injury has been related to differences in the fraction that is bioactivated to the reactive metabolite N-acetyl-p-benzoquinoneimine (NAPQI). Physiologically-based pharmacokinetic modelling was used to identify doses of APAP (300 and 1000 mg/kg in mice and rats, respectively) yielding similar hepatic burdens of NAPQI, to enable the comparison of temporal liver tissue responses under conditions of equivalent chemical insult.