In order to study the extent of utilization of various habitats by _Microtus_, a number of areas were sampled with Museum Special snap-traps. These traps were set in linear series approximately 25 feet apart. The number of traps used varied with the size of the area sampled and ranged from 20 to 75. The lines were maintained for three nights. The catch was assumed to indicate the relative abundance of _Microtus_ and certain other small mammals but no attempt to estimate actual population densities from snap-trapping data was made. In August, 1952, when the live-trapping program was concluded, the study areas were trapped out. The efficiency of the live-trapping procedure was emphasized by the absence of unmarked individuals among the 45 voles caught at that time. Further details of the methods and procedures used are described in the appropriate sections which follow. HABITAT Although other species of the genus _Microtus_, especially _M. pennsylvanicus_, have been studied intensively in regard to habitat preference (Blair, 1940:149; 1948:404-405; Bole, 1939:69; Eadie, 1953; Gunderson, 1950:32-37; Hamilton, 1940:425-426; Hatt, 1930:521-526; Townsend, 1935:96-101) little has been reported concerning the habitat preferences of _M. ochrogaster_. Black (1937:200) reported that, in Kansas, _Microtus_ (mostly _M. ochrogaster_) preferred damp situations. _M. ochrogaster_ was studied in western Kansas by Brown (1946:453) and Wooster (1935:352; 1936:396) and found to be almost restricted to the little-bluestem association of the mixed prairie (Albertson, 1937:522). Brumwell (1951:213), in a survey of the Fort Leavenworth Military Reservation, found that _M. ochrogaster_ preferred sedge and bluegrass meadows but occurred also in a sedge-willow association. Dice (1922:46) concluded that the presence of green herbage, roots or tubers for use as a water source throughout the year was a necessity for _M. ochrogaster_. Goodpastor and Hoffmeister (1952:370) found _M. ochrogaster_ to be abundant in a damp meadow of a lake margin in Tennessee. In a study made on and near the campus of the University of Kansas, within a few miles of the area concerned in the present report, Jameson (1947:132) found that voles used grassy areas in spring and summer, but that in the autumn, when the grass began to dry, they moved to clumps of Japanese honeysuckle (_Lonicera japonica_) and stayed among the shrubbery throughout the winter. Johnson (1926:267, 270) found _M. ochrogaster_ only in uncultivated areas where long grass furnished adequate cover. He stated that the entire biotic association, rather than any single factor, was the key to the distribution of the voles. None of these reports described an intensive study of the habitat of voles, but the data presented indicate that voles are characteristic of grassland and that _M. ochrogaster_ can occupy drier areas than those used by _M. pennsylvanicus_. Otherwise, the preferred habitats of the two species