useful "integrating dosimeters" that would provide information relative to whole-body exposures in the range of 100 or more mGy. Such evaluations would not provide relevant information regarding localized dose to the thyroid or to other organs resulting from internal deposition of radionuclides. 6.2.2 The Need for Baseline Data Information should be collected on baseline or background frequencies of various types of chromosomeaberrations and micronuclei in cultured lymphocytes in the particular population having suspected exposures. Careful, unbiased, selection of age-and sexmatched controlindividuals would be imperative if biomarkers were to be used to estimate levels of whole-body exposure to penetrating external radiations. Such data would be particularly important in a group such as the Marshallese since the inhabitants of the islands are genetically isolated and consanguinity is common, and as discussed in Section 5.5.11, the general health status of the population could be a potential confounderin interpretation of cytogenetic findings. 6.2.3 Preservation of Tissue If such an accident occurred today, it would be prudent to establish a repository of cryopreserved tissue samples from both exposed and non-exposed persons that would provide material for detailed study at some time in the future. Purified preparations of peripheral blood lymphocytes could be preserved for viability and maintained in liquid " nitrogen, whereas other nucleated blood cells could simply be frozen to provide DNA for analysis. i) ont tx3 om Gri 41