on July 18, 1957, a collection was made in the channel off the northwest end of Kabelle Island, Rongelap Atoll. All fish were obtained in water 15 feet or less in depth, and the collections were madein localities al- most identical to those of the 1954, 1955 and 1956 surveys. Locality, date of collection, common names, genera, species and number of specimens for the 1956 and 1957 collections are listed in the appendix. The fish were placed on ice in insulated containers within two hours of capture and transported to the Eniwetok Marine Biological Laboratory where they were frozen. There the fish were identified and dissected, except in the case of fish collected in 1956 when the frozen fish were shipped to the base Laboratory at the University of Washington for dissection and subsequent radiological analysis. Tissues used for analysis were muscle, bone, liver and stomach contents or viscera. Specimens which were too small to dissect were processed as whole fish. Partly because of the omnivorous food habits of the Marshallese natives and partly because of variations in the samples, it is advisable to analyze many specimensof a variety of species to obtain reliable estimates of levels of radioactivity (Welander, 1957). Consequently, two- gram samples of muscle tissue were taken from each fish and the aggregate was homogenized in a Waring Blendor. Plates were made of aliquots of this homogenate and the remainder dried for radiochemical analysis. All samples were dried at 100° C and the plated samples ashed at temperatures up to 540° C, cooled, slurried, dried and counted Cd oye . in