Islands. There have been conflicting reports in the literature concerning the relationship of potassium to cesium-137 uptake in plants (Auerbach and Croasley, 1958; Nishbita, et al., 1958; Uhler, 1959; Nishita et al., 1959). Apparently the uptake of cesium-137 by plants is directly as- sociated with potassium uptake in some cases and not in others. It was suggested from the results of studies of Coenobita at Eniwetok Atoll that seasonal differences in precipitation might influence cesium- 137 levels in muscle tissue (Held, 1960}; the data presented here do not support this suggestion. MATERIALS AND METHODS Samples of Birgus muscle were collected from Kabelle, Rongelap, and Eniaetok Islands at Rongelap Atoll during March 1958, August 1958 and March 1959. Two samples were also collected at Utirik Island, Utirik Atoll (Fig. 1) in March 1959. The samples were oven-dried at 98°C and the wet weight to dry weight ratios were determined. For potassium analysis, the samples were wet ashed with concentrated HNO3 and H209. The ash was dissolved in a known volume of IN HNO3 and the potassium content determined by flame photometry. Details of the method used have been reported by Chakravarti and Joyner (1959). The levels of cesium-137 were determined by gamma Five to ten-gram samples of dried muscle were counted. spectroscopy. The counting 0 prewy