Sah pe Atatea -20there is what might be called a strontium, cesium food cycle on land and a cerium food cycle in the lagoon. Summary 1. Periodic determinations of radioactivity in land crabs from Belle Island, Eniwetok Atoll, were made over a period of nearly two years following the 2954 atomic testing program. 2. Radioactivity in the exoskeleton was found to be due almost entirely to radiostrontium and the x79 daughter of gr?° and remained at a nearly constant level, excepting physical decay. 3. An estimate of contributions of rediostrontium from previ- ous tests to crab skeleton at Belle Island is given. 4, Long-lived fission products in muscle tissue consisted of 84 per cent cst37, 10 per cent gr904 ¥90 and 1 per cent Cel44 + ppl44 5. A possible association between the availability of cesium and rainfall is suggested. 6. During the first 150 days following a nuclear detonation the rate of decline of radioactivity in organisms on an atoll island may be considered to approximate the rate of decay of mixed fission products. 7. In so far as the long-lived fission products strontiun, cesium and cerium are concerned there appears to be 4 strontiun, cesium food cycle on land and 4@ cerium food cycle in the lagoon. nor