ABSTRACT The radiological contamination of Rongelap and Ailinginae Atolls in the eastern Marshall Islands has been evaluated from samples of material collected and from surface readings, The results of expeditions sponsored by the United States Atomic Energy Commission, Division of Biology and Medicine, and carried out by the Applied Fisheries Laboratory, University of Washington, between March 26, 1954 and June 30, 1955 are summarized in UWFL-42, Additional observations and collections made during October- November, 1955, are evaluated in this report. The decline of the radioactivity was found to be -1.75, i.e., r= 71.75 and steeper than the rate of decay for mixed fission products at a year and one-half (-1. 55). The radioactive content of most samples collected from the northern part of Rongelap Atoll continues to be higher than similar samples from the southern part of the atoll. The birds continue to be an exception to this generalization. Soil and lagoon bottom samples were collected extensively during October-November, 1955. These samples show great variability. Activity levels in the top 3 inches of soil at Kabelle and Labaredj Islands varied from 4,4 to 11.5 uwc/kg. The highest value (20.3 uc/kg) of any soil sample of the October-November collections, oddly, was found in the top 3 inches of soil from Rongelap Island. Other Rongelap Island values averaged