ACKNOWLEDGEMENTS The cooperation of all members of the staff of the Laboratory of Radiation Biology and the support of the Division of Biology and Medicine, Commission, U. are hereby acknowledged. S. Atomic Energy Dr. Lauren R. Donaldson and Dr. Edward E. Held supplied the samples from the islands and atolls outside the Eniwetok Test Site. Mr. Timothy Joyner, Mr. William Champion, Mr. Mr. Ronald Eisler, James Kimmel, and Dr. Arthur Welander helped in the collection of the plankton samples. Mr. William Tammany, logical Safety Division, the Yellowwood crater. gamma spectrum analyses. manuscript. Holmes and Narver Radio- supplied the bottom sample from Mrs. Marilyn Christ assisted in the Miss Marion Chase edited the final The cooperation of staffs of the Eniwetok Field Office, Task Group 7.1, and Holmes and Narver greatly facilitated the field operations.