POTASSIUM AND CESIUM-137 IN BIRGUS LATRO (COCONUT CRAB) MUSCLE COLLECTED AT RONGELAP ATOLL INTRODUCTION Rongelap Atoll was contaminated with radioactive fallout resulting from the Bravo test on March 1, 1954, to the extent that it was neces- sary to evacuate the population of 82 Rongelapese. lese returned to Rongelap in June 1957, safe for human habitation. Some 200 Marshal- after the area had been declared Since 1954, there have been several surveys to determine the level of radioactive contamination of the biota at Rongelap Atoll (Dunning, 1957). In March 1958, a long-term study of the ecology of the atoll, relative to radioactive contamination, was initi- ated at the request of the U S. Atomic Energy Commission, Division of Biology and Medicine. The objective of this investigation was to determine the radiocesium and stable potassium content in the muscle of Birgus latro (coconut crab) and to evaluate the relationship between the two, if any, under the ex- isting conditions at Rongelap Atoll. Birgus latro, the coconut crab, is of particular interest because it is edible and is a land crab known to contain cesium-137 in its muscle tissue. Cesium-137 is also the principal long-lived (27 years half life) fission product found in plants on contaminated islands in the Marshall