Technical Abstract: HiMag tall fescue (Lolium arundinaceum (Schreb.) S.J. Darbyshire = Festuca arundinacea Schreb) was selected for high Mg concentration to reduce grass tetany risk to ruminants; however, the mechanism of increased Mg uptake into shoots is unknown. The objective was to determine cation concentrations of roots, crowns, and leaves in plants of cv. HiMag and its parents, cv. Kentucky 31 and cv. Missouri 96, grown in nutrient solution for 42 days, and evaluate cation ratios due to translocation. Treatments were "basal" (1.5 mMK and 0.5 mM Mg), "K" (3.2 mMK), "Mg" (1 mM Mg), and "K+Mg" (3.2 mMk and 1 mM Mg). For HiMag, Mg was lower in roots (Trial 2 only), not different in crowns, and greater in leaves than Kentucky 31 and Missouri 96. Doubling nutrient solution's K and Mg from basal levels resulted in a 44% reduction of root Mg in Kentucky 31 and Missouri 96, compared to a 17% reduction in root Mg for HiMag. The basal K inflow rate for HiMag was lower than that for Kentucky 31 and Missouri 96. These results provide evidence for a process that limits K uptake and an active Mg translocation mechanism in tall fescue. HiMag was apparently selected for traits which promote translocation of Mg from roots to shoots.