In this research we examined the influence of chronic retrovirus infection on the hepatic metabolism of a model substrate, acetaminophen (APAP), and its induced liver injury in mice inoculated with LP-BMS murine leukemia viruses. Female C57BL/6 mice at 15-17 wks after LP-BMS retrovirus inoculation and age-matched control animals were used in the studies. APAP treatment (300 mg kg-I, p.0.) resulted in moderate to severe centrilobular necrosis in control animals, with the necrotic area accounting for 4040% of the total area. In contrast, the APAP-treated (300mg kg-I, p.0.) infected animals exhibited mild zonal necrosis with the necrotic area accounting for 1 4 % of the total area. In the same study, a statistically significant higher percentage of APAP glucuronide and a lower percentage of unchanged APAP were recovered from the urine of the LP-BMSinoculated animals than from that of controls. No statistically significant differences between infected and uninfected animals in the urinary recovery of APAP sulfate, APAP cysteine, or APAP mercapturate were observed. The formation of APAP metabolites and APAP-associated biochemical changes were also determined from liver slice preparation to avoid in vivo complicating factors. Consistently more significant depletion of the intracellular glutathione levels and K + content were observed in slices from the uninfected animals at high concentrations of APAP (1 and 2mM) than in slices from the retrovirusinfected animals. The differences in APAP-associated biochemical changes were accompanied by a 14-1.5-fold increase in the formation of APAP glucuronide, sulfate, and glutathione metabolites in slices prepared from animals inoculated with LP-BM5. We concluded that, based on histological examination and hepatic biochemical measurements, the retrovirus-infected animals were more resistant to APAP-induced liver injury. This could be due, in part, to alterations in the detoxification and activation metabolic pathways of APAP.