ABSTRACT Radiobiological analysis of the reef fishes of Rongelap and Ailinginae Atolls indicated that a recontamination of the area oc- curred in 1956 Gross levels of beta activity in muscle tissue ranged from 0 016 to 0 038 uc/kg wet weight. The levels of radioactivity in bone and muscle tissues of fish collected during 1957 were about the same as the levels for similar tissues collected in 1955. Gamma apectra analysis and ion-exchange methods revealed the presence of Zn®5, Co97, Co58, Co680, Mn54, and Fe55, Radiostrontium was found only in small amounts (about . 0014 uc/kg wet weight) in the bone of fish from Kabelle Island, Rongelap Atoll. Approximately 40 per cent of the total radioactivity in the reef fishes was due to Zn§5 28 per cent to cobalt, 26 per cent to Fe°>, and 6 nee eee ane, per cent to other radionuclides.