af tnjections (Scott et al., 1948), or after oral administration (Hamilton, ~~: 1947). From each mode of exposure, roughly two-thirds of the assimilated plutonium deposited in the skeleton, while the liver generally received the next highest foncentration of the radtonuc} ide. Plutonium was found to be so poorly taken up fram the gastrointestinal tract that only 0.007 per cent of an orally administered amount was absorbed. Of that which was absorbed, 65 percent was deposi{ted in the skeleton. Removal from the skeleton was very slow (Hamilton, 1947). Intravenously injected plutonium had its Mighest immed{ate concentration in liver and spleen. Later, it was translocated to bone (Brues et al, 1947). The distribution and elimination of plutonium was also studied after rats were exposed to it by inhalation (Scott et al., 1949). After nose-only ex- ee pe le posures of several minutes’ duration, most of the radioactivity was in the head and Jungs, but after 4 days, the Jungs contained most of the res tdual activity. study. The lung concentration declined over the course of the 64-day After 64 days, 12 percent of the plutonium inhaled as plutonium nitrate was in bone, canpared to 0.4 per cent of that inhaled as piutonium dioxide. The metabolism of plutonium was also studied in 18 human subjects injected with tracer doses of 239Py fn 1985 and 1946. As reviewed by Durbin (1972), bone and liver were shown to be the principal sites of plutonium deposition. Plutonium metabolism in pregnant rats and mice was also studied (Finkel, 1947). A very small fraction of Injected plutonium was found to move across the placenta. Studfes of factors Influencing the metabolism and deposition in bone of several radionuclides, isotopes of plutonium, strontium, yttrium and cerium