The absorption of Mn by excised rice roots was studied in the absence and presence of interfering cations like Ca, Mg, and Zn in the absorption medium. In the low concentrations of Mn, the uptake was competitively inhibited by 0.5 mM Ca or Mg, and Mg was slightly stimulatory on the absorption from high Mn concentrations. There was no significant interaction between Ca and Zn, Fe or Mg, on the absorption from 0.1 mM MnSO4, although these elements reduced the uptake, when present individually. The absorption of Mn from high concentration (5 mM) was enhanced by the presence of low amounts of ? or Mg (0.05 to 0.5 mM).