Exposure of rats to high dietary levels of sodium saccharin (NaSac) started in utero produce physiological effects at 30 days post-birth that are similar to those found in pups of iron-deficient dams. These similarities suggest that some of the changes due to NaSac are secondary to iron deficiency. The present experiment investigated whether the effects of 7.5% dietary NaSac in the newborn rat could be prevented by dietary iron and/or folate supplementation. The NaSac-related effects prevented by iron supplementation included anaemia, decreased serum iron and folate, increased serum cholesterol and triglyceride and increased serum vitamin E. Folate supplementation prevented NaSac-induced depression of serum folate and increase in serum vitamin E. Although bladder hyperplasia was increased by dietary iron and/or folate supplementation, the majority of the urinary chemistry changes associated with NaSac treatment were not affected. The results show that some physiological changes associated with NaSac treatment in the newborn rat may occur as a consequence of iron deficiency rather than a direct effect of NaSac treatment. These changes may be independent of the urinary and bladder effects, which are not reversed by iron supplementation.