Effects of different types of human activity on populations of medium-sized mammals were examined by counting road kills in the Central Valley of California. The mean number of road kills recorded from July 1997 to August 1999 was 1.2/100 km, most being black-tailed jackrabbits (Lepus californicus). Road kills showed no marked seasonal trends. For some species habitat type influenced where carcasses were located, carnivores being found predominantly in rural habitats. For other species, such as Virginia opossums (Didelphis virginiana), domestic cats (Felis catus) and rats (Rattus rattus), carcasses were located in both rural and suburban landscapes. Some important assumptions notwithstanding road kill data can be effective in discerning how mammals are influenced by different types of land use.