-35~— 3. The radioisotopic com»osition of the plankton and other marine organisms was determined by means of ion-exchange separations and gamma spectrum analyses. 4, Np239 was the major radioisotope present in all of the samples, contributing more than 50 per cent of the total radioactivity. 5. Other radioisotopes present in the plankton in the order of contri- bution were: Te 132-7132 Mo99- Te99™ | Bal40-7,4140. 237 Cel41- prl41 Ry103-Ry103, 7y95_yp25 and Cel44-prl44, Ryl05-pyl05 and Rul06-pn196 were detected only once. a 6. Small whole fish contained essentially the same radioisotopes as the plankton. A liver sample froma large dolphin (fish) contained only Np239 Ru!03_Rp103 and Te 132.7132. 7. Shrimp and squid samples concentrated Np239 but contained no Mo29-Tc99™ , and Te132_7132