1. The establishment of permanent grids in one study area of NTS (Area 11) and two study areas of TTR (Double Track and Clean Slate 3). These areas are the most accessible and continuous sampling would be facilitated. 2. Each study area would have two separate permanent grids, one for establishing residency of animals which can then be sacrificed for radioanalysis, histopathology, or blood sampling and one for monitoring population densities including reproduction, recruitment, and mortality. 3. In study areas of low priority in which previous sampling has been done, the resident animals will be sacrificed to increase the number of samples for radioanalysis. Data indicating preferential uptake of Am are interesting in light of data presented by Fowler and Essington (1974) on Am movement in the soil. An analysis of Pu and Am in rodent burrows would provide additional data on availability and uptake of Am in this microhabitat. Correction of sampling problems is now under consideration. 63