Cytogenetic studies based upon somatic cells (bone marrow) have disclosed that the marmot hitherto designated Marmota caligata broweriHall and Gilmore, occurring in the Brooks Range of arctic Alaska, differs from M. c. caligata (Eschscholtz) in number of chromosomes (2n=36 as compared with 2n=42 in M. caligata) and in proportions of chromosomal types. Typical karyograms for the two species are presented. It is concluded that the Brooks Range marmot is specifically distinct from M. caligata, the applicable name being Marmota broweriHall and Gilmore. Also determined were diploid chromosome numbers for two other Nearctic species of marmots, M. flaviventris (Audubon and Bachman), with 42, and M. olympus (Merriam), with 40. It is suggested that M. broweri survived the last (Wisconsin) glaciations in the amphi-Beringian refugium, and that its closest affinities may be with one of the Eurasian species of Marmota.