INTRODUCTION The Brookhaven National Laboratory Radiological Surveillance Program in the Marshall Islands includes the quantitative assessment of internally deposited radioactive material in the Marshallese. In, this report, the results of four whole body counting measurements on the Bikini population that were conducted in 1974, 1977, 1978 and 1979 are presented. Because the body burden measurements were per- formed by two different organizations, the current experimental de- sign included a cross check mechanism to ensure that previous and ' current results are directly comparable. was multidirectional. duplicated. (CO 63). The approach to the problem First, key detection components were Second, the systems were calibrated in the same manner Third, the operational procédures and counting geometries were basically similar, and duplicate counts were made on Brookhaven personnel with known. body burdens to ensure total system comparabil- ity. EXPERIMENTAL DESIGN A. Instrumentation The detector chosen for field use by both Brookhaven organiza- tions is a 28 cm diameter, 10 em thick, sodium iodide thallium activated scintillation crystal NaI(Tl). It is optically coupled to seven, 7.6 cm diameter low background magnetically shielded, photomultiplier tubes. In the current system the signal output from each photomultiplier tube is connected in parallel through a summing box with the combined output routed to a preamplifier/amplifier and