EN
Relations of particular genera of Monocercomonadidae and Trichomonadidae with groups of hosts are discussed. Main hosts of these flagellates are insects (mainly termits) and cold-blooded vertebrates (amphibians and reptiles); the proper location within the host body is the intestine. Some representatives of these flagellates have changed their host and location and occur now in warm-blooded vertebrates (birds and mammals) and in man, usually in organs other than the intestine. Change of localization within the host body is probably responsible for growing pathogenecity of these flagellates.