-6put on ice as soon as possible after collecting and placed in a freezer on being returned to the laboratory. Tissues were dissected, weighed, and dried at the Eniwetok laboratory. tissues taken were skin, muscle, bone, The liver and viscera (diges- tive tract and contents) from the larger fish, or like tissues were pooled from a number of small fish of the same species,or entire fish were used. laboratory, 540° C, At the University of Washington the dried samples were ashed at temperatures up to cooled, slurried, dried and counted in an internal gas- flow counting chamber. The total number of plates resulting from all 34 collections was 2,167 (averaging about 64 plates per collection). All counts for radioactivity were corrected to the date of collection, the decay factors for all Eniwetok samples being based on a soil sample collected at Belle Island May 15, 1954. Corrections were also made for self-absorption, backscatter, geometry and coincidence. The radioactivity is expressed in microcuries per kilogram of wet tissue. Disintegrations per minute per gram can be converted to microcuries per kilogram using the relationship uc/kg = (2.2) (10)3 d/m/g. Results Trends or Decline in the Levels of Radioactivity General trends of the radioactivity in the fish collected at Belle Island are shown in Figure 2. Lines connecting the points for data on muscle and liver tissue reveal trends similar