A total of 1296 free-living mammals and birds of 12 species was examined for serologic and bacteriologic evidence of leptospiral infection. Endemic infection with serovar ballum was found in several introduced species of mammals. Endemic ballum infection is not recognized in the same species in Great Britain, their country of origin. Possums (Trichosurus vulpecula) were found to have a high prevalence of infection with balcanica, a serovar that has been isolated from possums in Australia and from cattle, pigs and humans in Eastern Europe. Free-living lagomorphs and deer were both serologically and bacteriologically negative. Waterfowl were bacteriologically negative, and only one serological titre was found.