Tae present report gives available data through 1958 including a reevaluation of 1954-55 counts upon which UWPL-42 243 reported, put using ash welght as well as wet weight, with a modification of results, and a comparison of activity yielded by fine-mesh as contristec with coarse-mesh plankton nets. The rate of physical decay change, herein terme. of early s:mples is comozired with the rate ofdecline ,of successive samplings at later dates, up to more than four years after the original fallout. Methods of collecsins and prtessing of the 1954-1955. materials are G-sectibed in UWFLe42:3> and UWFL-43:44. leesing In 13956 and 1957, col- lffe red from that of previcus years in that amphibious air craft or ruber btoavs vere used for towing tne nets. Methods of vrocecsing wore uncthanzed. In 1953, plankton tows were mide with 1/2-meter nylon nets of 7-80 meshes per inch by towing from an LSVF (March) or ea DUKY (August) for fro.a 10 to 30 minutes at a velocity of 24: -3 miles per hour during davitgnt, and within 3 (usually 1-2) miles of the localities indicated in Table 2. In August 1958, only, plankton was also collected from the Sipe] eee "Aloto" by means of pumping which not only permitted a more precise measurement of volume of sea water filtered, and pin-pointing of locaticn of tne sampling station than is possible with tows, but also allowed simultaneous sampling of tne lagoon-bottom material. Thus, .