This study was designed to estimate the impact of pollution resulting from the meltdown of Reactor 4, Chornobyl, Ukraine, on the taxonomic diversity and abundance of small mammals in the surrounding area. Trap sites included the most radioactive areas within the 10-km exclusion zone, a site within the 30-km exclusion zone that received minimal radioactive pollution, and five sites outside of the 30-km exclusion zone. Within the exclusion zones, 355 specimens representing 11 species of small mammals were obtained, whereas 224 specimens representing 12 species were obtained from outside the exclusion zone. It is concluded that the diversity and abundance of the small-mammal fauna is not presently reduced at the most radioactive sites. Specimens from the most radioactive areas do not demonstrate aberrant gross morphological features other than enlargement of the spleen. Examination of karyotypes does not document gross chromosomal rearrangements.