The use of disturbed areas was probably important in the recent invasion of hispid cotton rats into north-central Kansas from the northern presettlement limit of their range in Oklahoma. On Texas rangelands, hispid cotton rats appeared to respond to increased biomass of standing crop and increases in the proportion of the standing crop in potential food plants such as bristlegrasses ("Setaria" spp.). Rat density was four times greater on areas planted to exotic grasses including King Range bluestem ("Bothriochloa ischaemum") and buffel grass ("Enchrus ciliaris") than on native range dominated by windmill grass ("Chloris" spp.) and Texas wintergrass ("Stipa leucotricha").