in large amounts, may escape detection unless a combination of various methods is used. For example, the predominate radio- isotope in the first analysis of the kidney of a giant clam from the Marshall Islands was found to be radiocobalt. radioisotope of iron. (Fe?) However, a which emits a weak X-ray (see Table 1) was present but was not detected by the original gamma spectrum analysis. Fe” was used, When the proper technique for identifying radioiron was found to be in greater abundance than radiocobalt (Table 2). plankton. Another example is that of the Taney Gamma spectrum analysis of a sample in November, 1957 confirmed the earlier finding that the major fission products were cet44_p, 144 but also revealed an appreciable amount of C08? (Lowman et al.,1958). Modification of techniques to meet the special requirements of an analysis is sometimes required. In order to accurately determine sr?° in marine organisms, especially fish, a special technique was developed by Kawabata and Held (1958). As these special techniques develop and the detection equipment becomes more sensitive, more isotopes can be expected to be found or to be determined more accurately. The time after fallout when the sample is collected demands consideration when the results of radiological analyses are being compared because the relative composition of the radioisotopes in a sample of mixed fission products is constantly changing (Table }. It is obvious that the comparison of the relative radioisotopic