35 SUMMARY Rongelap Atoll received a single heavy dose of radioactive fallout in 1954. The atoll soils are calcareous and contain no inorganic colloids; the exchange capacity is related to organic content. Comparison of gamma-ray spectra of depth increments from old and new soils shows that Cs L137 and Sb 125 move most readily in the old soil; the principal gamma-emitting radionuclide moving in new soil is sp??? , sr?? moves in both old and young soils. The distribution of radionuclides at the surface is very spotty. There is a vertical gradient in the distribution of radionuclides within the surface one-inch layer. Litter redeposits Cs 137 and Sr 90 . over the soil surface and eRRE FEE re e bird droppings have added zn°> and co°?, The principal reservoir of radionuclides in young soils is + the surface algal crust. In eroded areas radioactivity is associated with large coral fragments, which are infiltrated with algae. 10. There is some localized horizontal movement of radionuclides in old soils. Coke