Acetaminophen (APAP) produced renal necrosis restricted to the straight segment of the proximal tubule in Fischer 344 (F344) rats but not in Sprague-Dawley (SD) rats. APAP-induced renal functional changes (elevation in blood urea nitrogen and reduction in the accumulation of p-aminohippurate by renal cortical slices) also correlated with strain-dependent histopathological changes. Such strain differences have been attributed to differences in renal P-450 activation of APAP or the deacetylation of APAP to the nephrotoxic metabolite, p-aminophenol (PAP). Kidneys from F344 rats displayed greater concentrations of P-450 and greater ethoxycoumarin-o-deethylase activity than kidneys from SD rats. However, covalent binding of [ring-14C]APAP to renal and hepatic microsomal protein in vitro was similar for both SD and F344 rats. Deacetylation of APAP to PAP was similar in renal and hepatic homogenates from SD and F344 rats. Furthermore, isolated kidneys from SD and F344 rats perfused with APAP excreted PAP at similar rates. PAP excretion, over a 24-hr period following APAP administration, was greater in F344 rats than in SD rats only at the highest dose (900 mg/kg) of APAP. Thus, strain differences in APAP-induced nephrotoxicity apparently cannot be attributed to differences in P-450 activation of APAP or in deacetylation to the nephrotoxic metabolite, PAP.