Perfusion of livers from fed and fasted rats with 0.07--0.1 mM t-butyl hydroperoxide for 15 min decreased the levels of reduced glutathione (GSH) by 1.5 mumol/g liver in both nutritional states. Glutathione disulfide (GSSG) was increased by 70 and 140 nmol/g liver and glutathione mixed disulfides enhanced by 45 and 150 nmol/g liver in livers from fed and fasted animals, respectively. The ratio of GSH/GSSG was decreased from 243 to 58 in fed animals, and from 122 to 8 in fasted animals. The increase of GSSG and the mixed disulfides was nearly parallel until an apparently critical low GSH content of 1.5 mumol/g was reached. Only in livers from fasted rats 14CO2-production from [1-14C]glucose was stimulated upon t-butyl hydroperoxide infusion at the employed rates. Flux of glucose through pentose phosphate cycle rose from 8 to 12% of glucose utilization via glycolysis, whereas in livers from fed animals this portion remained unchanged at 8% Dithio-erythritol reversed pentose phosphate cycle activity as well as GSSG and protein-bound glutathione contents to the original levels. In livers from fasted rats the activity of glucose-6-phosphate dehydrogenase was increased by 34% by t-butyl hydroperoxide infusion.