Coyotes, house cats and raccoons were identified as predators on voles in the study areas. Remains of voles were present in 12 per cent of the scats of the coyote (_Canis latrans_) examined. In Missouri, Korschgen (1952:40-43) reported remains of voles in slightly more than 20 per cent of the coyote stomachs that he examined. Fitch (1948:74), Hatt (1930:559) and others have reported other species of _Microtus_ as eaten by the coyote. Although coyotes were rarely seen on the Reservation, coyote sign was abundant (Fitch, 1952:29) and coyotes probably ate large numbers of voles. House cats (_Felis domesticus_), seemingly feral, were observed to tour the trap lines on several occasions and were noted by Fitch (_loc. cit._) as important predators on small vertebrates. Four cats were killed in the course of the study and remains of voles were found in the stomachs of all of them. On several occasions, raccoon tracks were noted following the trap line when the traps had been overturned and broken open, suggesting that raccoons are not averse to eating voles although no further evidence of predation on voles by raccoons was obtained. Fitch (_loc. cit._) reported raccoons (_Procyon lotor_) to be moderately common on the Reservation. Reports of predation by raccoons on voles are numerous (Hatt, 1930:554; Lantz, 1907:41). The opossum (_Didelphis marsupialis_), common on the Reservation, occasionally eats voles (Sandidge, 1953:99-101). Other mammals which are probably important predators on voles on the Reservation, though no specific information is available, are the striped skunk (_Mephitis mephitis_), spotted skunk (_Spilogale putorius_), weasel (_Mustela frenata_) and the red fox (_Vulpes fulva_). Eadie (1944; 1948; 1952), Shapiro (1950:360) and others have reported that the short-tailed shrew (_Blarina brevicauda_) was an important predator on _Microtus_. Shrews were present on the Reservation but were not trapped often enough to permit study. The variety of vertebrates preying on voles suggests that they occupy a position of importance in many food chains. Errington (1935:199) and McAtee (1935:4) refer to voles as staple items of prey for all classes of predatory vertebrates. An attempt to evaluate prey species was made by Wooster (1939). He proposed a formula which involved multiplying the density of a species, its mean individual weight, the fraction of the day it was active and the fraction of the year it was active to give a numerical index of prey value. Although his methods of determining population densities would now be considered questionable, the purpose of his investigation merits further consideration. He reported _M. ochrogaster_ to be second only to the jack-rabbit (_Lepus californicus_) as a prey species in west-central Kansas. MAMMALIAN ASSOCIATES