The measurement of endogenous substances that function as biological antioxidants is of importance because the values obtained might be an index of future health. We quantified three water-soluble antioxidants by high-pressure liquid chromatography with electrochemical detection (h.p.l.c.-e.c.). Current-voltage relationships made at various settings of the D2 porous graphite electrode help to identify ascorbic acid, glutathione and uric acid. The antioxidants are determined simultaneously and without need for derivatization. The method is seen to be useful for comparison of normal rat liver with liver that had undergone oxidative stress through ischaemia. Antioxidant levels in liver, kidney, pancreas and intestinal mucosa are presented and compared with literature values. Endogenous contents of oxidized forms of ascorbic acid and glutathione become apparent following exposure of tissue samples to a strong reductant such as 2-mercapthoethanol.