54Mn present in the first two leaves of oat seedlings subsequently deprived of manganese was later redistributed to leaves 4 and 5. 54Mn was found in leaves 3 and 4 even when the roots of seedlings were excised immediately after exposure to 54Mn, but more was detected if the roots were left intact. 54Mn applied as a drop to the 4th leaf of manganese-deficient oat plants was concentrated in the stem and translocated primarily to the youngest developing leaf or to the grain if present. 54Mn was readily detected in the roots but almost none was translocated to the first three leaves. More 54Mn was translocated in 96 hrs. than 24, but little or no more was translocated in 192 hrs. Plants which were given 0.5 p.p.m. stable manganese until they reached the 4th leaf stage, and were then exposed to 54Mn, showed a fairly uniform distribution of 54Mn throughout the plant. There was relatively slight concentration at active growth centres. It is concluded that physiologically significant redistribution of manganese occurs in the oat plant.