When Trolox (a polar analog of vitamin E) is conjugated to p-aminophenyl-P-D-lactopyranoside, the resulting lactosylphenyl Trolox becomes a markedly more stable and effective hepatoprotector than Trolox. In primary rat hepatocytes exposed to xanthine oxidase-hypoxanthine, lactosylphenyl Trolox prolonged cell survival better than did Trolox, mannitol or ascorbate. In rats that underwent 80-min partial hepatic ischemia, infusion of lactosylphenyl Trolox at 2.9 to 5.7 pmol/kg body wt just before reoxygenation salvaged the organ more extensively than did Trolox. Mechanistically, we showed (a) that lactosylphenyl Trolox does not inhibit xanthine oxidase; (b) that lactosylphenyl Trolox effectively scavenges oxyradicals generated with xanthine oxidase and the peroxyl radicals produced with 2,2'-azo-bis( 2-amidinopropane) HCl; (c) that both in hepatocytes and in r h o , lactosylphenyl Trolox is distinctly more cytoprotective than either or both of its precursors; and (d) that lactosylphenyl Trolox is amphipathic (i.e,, it has both hydrophilic and hydrophobic properties), which enable it to better access and protect the lipid and aqueous milieus of the cell than the lipophile vitamin E and the moderately polar Trolox. Thus there are strong fundamental reasons for lactosylphenyl Trolox being an effective antioxidant-based hepatoprotector. (HEPATOLOGY 1992; 15:454-458.) Evidence increases showing that oxyradicals play a key role in diverse pathologies, including postischemic reperfusion injuries that may occur in hepatectomy or liver transplantation. This recognition has triggered active research into therapeutic antioxidants (1). Although vitamin E is a potent antioxidant, its apolarity and slow cellular uptake (2) limit its clinical utility, especially in emergencies. Scott et al. (3) prepared a polar analog of vitamin E called Trolox (TX), which scavenged peroxyl radicals in cell-free systems (4, 5 ) . Casini, Pompella and Comporti (6) noted that TX reduced liver damage in rats poisoned with substances such as