To investigate in vivo interactions between antioxidant vitamins C and E, sparing effects of vitamin C on vitamin E as well as those of vitamin E on vitamin C were evaluated using inherently scorbutic [Osteogenic Disorder Shionogi (ODS)] rats. Rats were divided into four groups (control, vitamin E-deficient, vitamin C-deficient and simultaneously vitamins C and E-deficient). The levels of vitamins C and E in tissues were determined at 0, 14 and 21 d of deficiency. On d 14, the vitamin E concentration in plasma, liver, brain and lung of the vitamin C-deficient group was significantly lower than that of the control, in agreement with the literature concerning the sparing of vitamin E by ascorbate. The vitamin E concentration of the vitamin C-deficient group also was significantly lower in plasma, heart, liver, lung and kidney than that of the control group on d 21. On the basis of two-way ANOVA, significant interactions between vitamins C and E were observed on d 21 for vitamin E concentration in these tissues. The ascorbate level in plasma, heart, liver, muscle and kidney of the vitamin E-deficient group was significantly lower than that of the corresponding control group on d 21. Significant interactions between vitamins C and E were observed on d 21 for vitamin C concentration in these tissues. These results suggest a sparing effect of vitamin E on vitamin C, an effect that was observed for the first time in this study. These results suggest that the interaction between vitamins C and E exists in vivo and that the extent of the interaction depends on the tissue. Thiobarbituric acid reactive substances (TBARS) in plasma and liver of the vitamin C-deficient rats were significantly higher than those of the control and the vitamin E-deficient groups on d 21, suggesting that the deficiency of vitamin C caused a larger increase in oxidative stress than the deficiency of vitamin E. TBARS of the liver in rats deficient in both vitamins C and E were significantly higher than those in all other groups, suggesting an additive effect of the deficiencies of vitamins C and E on hepatic TBARS. These data suggest that in vivo, vitamins E and C interact, and each can exert sparing effects in the absence of the other.