One thousand two hundred and sixty-nine freeliving, wild mammals, representative of 16 species from estates in Berkshire, Oxfordshire and Surrey, were examined for the presence of salmonellas. Salmonella typhimurium was isolated from 1 and S. dublin from 7 house mice (Mus musculus). There were no isolations from the other species examined. It was concluded that the house-mice infected with S. dublin acquired the organism from experimentally infected cattle. The wild mammal population does not at present appear to constitute a reservior for infection of domestic animals.