Field programs were initiated at both Enewetak and Bikini Atolls to specifically develop the data required to produce more precise radiological dose assessments dafid to define how the ecosystems operate. Major subsistence crops have been planted to determine the radionuclide concentration in the edible foods, define the time dependence of radionuclides in the atoll ecosysten, and develop concentration ratios (plant/soil) for predictive dose models. Additional research is designed to delineate the cycling of radionuclides to better understand the transport of elements in the atoll ecosystem and to evaluate potential remedial measures for reducing the uptake of critical radionuclides in the subsistence crops. Soil samples are analyzed as part of this program not only to develop concentration ratios but also to supply the necessary data to evaluate the inhalation pathway. Usable groundwater sites are identified and the radionuclide concentrations are carefully assessed since this water may be used in the future for drinking, household or agricultural purposes. In the marine environment fish, water and sediment samples are collected to determine the concentration of radionuclides for use in the dose assessments; in addition, the data are also used to develop predictive models for the marine pathway for remobilization of radionuclides from the sediment, lagoon flushing rates, concentration ratios for fish and water, temporal variations of radionuclides in lagoon water, etc. One of thecritical variables in any Marshall Island dose assessment is the assumed dietary intake for the population. Published data on the average annual intake of locally grown foods is very sparse. The estimated dose is directly proportional to the intake of local food products grown on the atolls. It has, therefore, been essential to attempt to develop information on the dietary habits of the residents of the various atolls; these studies have been very limited to date and need to be included as a major effort under P.L. 96-205. im