FA tee a me distinguished. The mean coefficients all He between 1.6 and 1.9 and unclassified biological types vary more than do classified types. CONCLUSIONS Open~sea marine plankton can concentrate faliout activity strorgly and thercfore should be included in fallout transport considerations and in plans for dieposal of atomic waste. This concentration is especially significant because it appears in an organic food. There is evidence from both beta and gamma analyses that certain plankton types have affinities for specific isotopes. The radioanalyses of the first two samples of contaminated oceanic zooplankton has not demonstrated that there exists a simple relationship between the affinity of a class of plankton toward radioactivity, and the size of food it apparently prefers to eat. There is more variability within the classes than between these classes. Ocesnic zooplankton appear to be very effective concentrators of materials that are lixely to be available in a particulate form, but they may concentrate certain other materials also, such as radiostrontium which is morelikely to be in ionic form. There is some evidence that the retention of finely dispersed activity varles more or less proportionally with the organism’s dry weight over a considerable range in body size, surface area, and water content. x! 17