GAM SERATESATRONGELAP-ATOLL,—1954~-1963 C~ ABSTRACT Y Rongelap Atoll was contaminated with fallout from a thermonuclear device on March 1, 1954. 3.5 r/hr to 35 r/hr. Gamma-dose rates on D + 1 ranged from Until 1959 the decline of gamma-dose rates measured in the field followed the theoretical decay of mixed fission products from u*>> calculated by Miller and Loeb. The reduction of gamma dose rates to approximately half the predicted levels in 1959-63 probably reflects the downward movement of the long-lived gamma-emitter cs}37 in the soil. Redistribution of fallout had little effect on gamma dose rates except in the intertidal zone. It is concluded that predicted gamma dose rates from fallout based on the theoretical decay curve of radio- nuclides from fission of p35 would tend to be equal to or greater than actual levels.