The reduced glutathione (GSH) levels in the hepatic tissues, extent of lipid peroxidation in the liver, kidney and brain, and alterations in the activity of glutathione peroxidase (GPX) in the hepatic tissues were monitored in mice bearing a transplantable ascitic lymphoma. These markers showed substantial alterations during the height of tumour progression when compared to controls. The GSH level, extent of lipid peroxidation, and GPX activity increased sharply after approximately 2 weeks following inoculation of ascitic cells. This was followed by a steady decline in all markers and death occurred around day 32 after inoculation.