Mycobacterium bovis infection has been confirmed in a wide range of mammals hosts throughout the world. The European badger (Meles meles) and the brushtail possum (Trichosurus vulpecula) are implicated as significant sources of infection for domestic cattle in the UK and New Zealand respectively. The risk of transmission of infection between a wildlife population and domestic animals will be determined by both the epidemiology of the disease and the ecology of the host. In the UK, surveys by the UK Ministry of Agriculture, Fisheries and Food (MAFF) have identified M. bovis infection in deer (Cervus sp., Capreolus sp., Dama sp.), red fox (Vulpes vulpes), mink (Mustela vison), feral ferret (Mustela furo), mole (Talpa europaea), brown rat (Rattus norvegicus) and feral cat (Felis catus). However, the potential contribution to cattle herd breakdowns, of reservoirs of M. bovis infection in mammals other than the badger is poorly understood and is the subject of current research. In contrast, M. bovis infection in the badger has been the subject of a long term ecological and epidemiological study at Woodchester Park in South-West England, where the prevalence and distribution of infection in a wild population has been intensively monitored. The pattern of infection in the population and potential risks to cattle, are profoundly influenced by badger social organization and behaviour. The pattern of land use and cattle farming practices in the UK brings badgers into close contact with domestic animals and provides conditions that may enhance the likelihood of disease transfer. Copyright 2001 Harcourt Publishers Ltd.