The overall goal of this project is the determination of human manganese requirements in light of the inadequacy of balance data. Thus the specific aims are: 1) to determine whether changes in manganese intake & tissue levels of manganese (Mn) have functional significance in rats & humans; 2) to assess the importance of endogenous gut losses of Mn in maintaining Mn balance & 3) to assess the mechanisms by which Mn & iron (Fe) interact. To accomplish aims 1 & 3, a series of rat feeding studies & a 125-day double blind clinical trial will be conducted. In Study 1 rats will be fed 3 levels of Mn (deficient, adequate, excessive) & 2 levels of Fe (marginally adequate & generous) for 60 days. Tissue Mn & Fe levels; the activity of MnSOD, catalase & CuZnSOD; lipid peroxidation; & the amount of Fe lost when mucosal cells are sloughed will be monitored. In Study 2, peroxidation stress to animals will be increased by feeding high levels of fats, particularly polyunsaturated fats, for 120 days. In Study 3 the effects of injected versus oral doses of Fe on Mn utilization will be investigated. MnSOD a catalase activity, lipid peroxidation, in vivo RBC t1/2, RBC fragility, TIBC & tissue levels of Mn & Fe on Mn utilization vivo RBC t1/2, RBC fragility, TIBC & tissue levels of Mn & Fe will be determined. In the clinical trial, 60 women will consume 60 mg Fe &/or 5 mg Mn or placebo tablets for 120 days. Nutritional status in regard to Mn (serum Mn, MnSOD) & Fe (serum ferritin, transferrin, TIBC), will be assessed regularly during the study. To accomplish aim 2 & further study aim 3, additional rat studies will be conducted. In study A the tissue distribution of Mn-54 injected intraportally in complexes with transferrin, delta macroglobulin, albumin or cysteine will be monitored. Those complexes, that result in the distribution of Mn-54 in tissues, will be used in Studies B & C to label tissues of rats fed varying levels of Mn & Fe. Then the effect of variations in Mn & Fe intakes on endogenous gut losses of Mn will be calculated.