ABSTRACT Three sections of subject matter are combined in this paper. Section I shows the pattern of radioactive decay over periods of about six years for 102 samples from Eniwetok Atoll, plus 2 sand samples from Nevada. from -1.2 to -1.8. Logarithmic plots commonly had slopes of The slopes for the last three years tended to be steeper and to show more variability than for the first three years. An exceptionally slow rate of decay, -0.06, prevailed for the last three years in a sample of rat muscle where Cs137 was almost the only radioisotope. ON peRte Slow decays occurred in muscle, liver, bone, and kidney of various animals. In Section II, available data on plankton from Rongelap Atoll for 1954-1958 are brought together, including not only values based on wet weight as reported earlier, but also new values computed on the basis of ash weight of sample, which gave more consistent results. Mesh size did not influence activity levels of the plankton samples. For August 1958, the amountof activity in 10 pumped plankton samples was shown not to be correlated with the activity of samples of lagoon bottom material taken at the same stations. -Lil-