Plutonium and polonium assays of the giant kelp revealed that most of the Pu and Po was in the surface scrapings. Both nuclides were concentrated to 1000 times their sea water concentrations; there was usually 200 times more Po activity than Pu. Field experiments using Macrocystis pyrifera showed that Pu and Po accumulated in proportion with time and surface area and that approximately four times more Pu and Po were found on oldest tissues. When glass microscope slides were exposed alongside living plants, deposition rates for Po were identical and Po deposited about 200 times faster than Pu. (HLW)