Selenomonas spp. were isolated for the 1st time from lesions and non-digestive organs which were apparently normal in 2 cows, 6 pigs and 1 human. Identification as Selenomonas was based on EM observation and on fermentation products. They were divided into 3 major groups by biological properties and by the patterns of these products. The habitats of organisms of the genus Selenomonas are generally digestive organs, including the rumen of the ruminant, the cecum of the guinea pig and the oral cavity of man. The existence of these organisms in lesions and non-digestive organs in such animals and man is unknown. The habitat of these organisms in swine is unknown. Selenomonas may invade other parts than the digestive organ in some animals and the organism may exist in the swine digestive organs. The role of Selenomonas as a secondary invader in some animals was proposed.