by the three stations with the greatest activity, or (3) by all stations gave the same order, with one exception, and was as follows: algae, invertebrates, plankton, fish, land plants and land vertebrates. The exception was that of the post shot land plants, which ranked third. The pattern of distribution of activity of the pre-shot collections clearly indicates the areas of former test sites Engebi, Aomon-Biijiri, and Runit. Pre-test collections at other stations had considerably less activity, which decreased with distance from the test site in the following order: ombogo, Runit, Igurin, and Japtan. Bog- The activity at Japtan Island was not much greater than that which would be expected from naturally occurring isotopes. An exception was the counts of plankton samples, which were greatest on the western side of the atoll. This distribution might be expected because of the move- ment of the surface currents from east to west. For the post test collections the center of distribution was shifted toward the site of the Mike shot. For the outlying stations there was again a marked decrease in activity but with greater activity, as related to distance from Mike site, western side of the atoll than on the eastern side. on the There was & slight but definite increase in activity at Japtan. The ratio of post shot to pre-shot activity as determined by the averages for each group of organisms was approximately 300 for the aquatic organisms and 1,000 for the land plants and vertebrates. - 106 -