AbstractThe status of the 15 species of exotic mammals naturalized in Britain is briefly reviewed along with the problems they cause and the costs of control. The legislation governing the keeping of exotic mammals is discussed and an assessment is made of the number of mammals kept in Britain for purposes other than food production. These include 3 200 000 kept for experimental purposes, over 12 848 in zoos, 100 000 Mink on farms and over 11 million households with at least one pet. The results of a recent survey of animals held in Britain under the Dangerous Wild Animals Act 1976 are presented; nearly 1000 individuals of at least 76 species are held under this legislation.Between January 1970 and October 1989, 293 exotic mammals, of 39 species not normally kept as household pets, were recorded out of captivity on 127 occasions. An analysis of the sources of these exotics and their subsequent fate is presented. It is suggested that monitoring the occurrence of exotic species out of captivity provides information on which species are most likely to establish feral populations in the future. This will allow preventive measures to be planned and their efficacy to be assessed before a new exotic species becomes established.