Small mammals, particularly the white-footed mouse, Peromyscus leucopus, were live-trapped, marked and released in a radiated, natural oak-pine community at Brookhaven National Laboratory. Studies during the summer of 1961 evaluated the population prior to the start of daily radiation in November, 1961. The population was then studied in the summer of 1962 during radiation. No detectable effects of radiation were observed in the population. Lack of detectable effects of radiation may be attributed to: (1) a low population density and too few animals with which to work, and (2) a local nonrandom orientation of this species to certain parts of the radiated forest which resulted in its being found in areas away from the source; that is, they were found where levels of radiation were mostly below 3 r/day. Habitat orientation in Peromyscus leucopus was found to be strongly associated with the 0.0-0.3 m shrub layer which consisted largely of Vaccinium angustifolium. Wherever cover of this shrub layer was thick, captures of the white-footed mouse were at a minimum. Higher capture success was recorded in areas where this shrub layer was not as abundant.