bathythermograph (BT) winch, was lowered rapidly to the desired depth, towed at this depth for designated periods varying from 15 to 125 minutes, and then raised rapidly to deck level. Haul depths from the surface to 457 meters were determined by the useofa BT. The volume of the sample was determined volumetrically by allowing the sample to settle for five minutes in a graduate cylinder. Details of the plankton hauls are given in Appendix Table A. In order to direct the movement of the ship while attempting to delineate the mass of radioactive water produced by the Wahoo detonation, a 5-cc portion of plankton samples P-22 to P-35 was filtered through a Millipore filter disc 47 mm in diameter (pore size 0.45), and the total gamma activity of the plankton was determined immediately on the wet sample. Island, Later, at the Eniwetok Marine Biological Laboratory on Parry the gross beta activity of the sample was determined on the dried material. In some samples the plankton were separatedinto "small" plankton. The “large" and sample was first filtered through a bronze screen 2-3/4 inches in diameter with a mesh of 99 to the inch (large plankton), and then through a Millipore filter disc with a pore size of 0.45u (small plankton). For the determination of gross beta activity,a portion of each sample was placed on a 1-1/2-inch stainless steel planchet, dried under infrared lamps, and counted aboard ship. The beta-counting equipment consisted VES Anes nor