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, U. S. Atomic Energy Commission, are hereby acknowledged. Dr. Lauren R. Donaldson and Dr. Edward E. Held supplied the samples from the islands and atolls outside the Eniwetok Test Site. Mr. Ronald Eisler, Mr. Timothy Joyner, Mr. William Champion, Mr. James Kimmel, and Dr. Arthur Welander helped in the collection of the plankton samples. Mr. William Tammany, Holmes and Narver Radio- logical Safety Division, the Yellowwood crater. gamma spectrum analyses. manuscript. 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. op ne por *