Current scientific opinion regards the Protozoa as a separate kingdom of one-cell eukaryotes, which consists, according to different authorities, of 7 to 45 divisions, with about 70000 species at present known worldwide. These organisms form an important group, with a large number of parasitic species, some the cause of human and animal diseases. Protozoan infections have become prominent because of the recent increase in problems of immuno-deficiency, but the practical importance of these organisms is not restricted to their role as agents of disease. Representatives of the Protozoa form a substantial part of the biosphaere and are an inextricable link in its trophic chain. Protozoa are very important in biological estimation of water quality, their presence is necessary in the processes of soil formation, and fossil Protozoa species are critical in stratigraphy. The study of biodiversity is a relatively new field, so not surprisingly existing information allows only a rough estimate of the species diversity of Protozoa in Ukraine. Although a number of prominent protozoologists worked in Ukraine (L.S. Tsenkovskyi, I.I. Mechnikov, V.Ya. Danilevskyi, D.F. Liambl etc.), the country's Protozoa remain poorly known. Only 1840 species of this group (excluding phytomastigins, and about 3% of the known world total) are known from Ukraine, and coverage of different groups varies greatly. The bulk of the known species (1083) belong in the group Infusoria. There are 50 known species of the naked amoebae, 226 species of the shelled amoebae (according to M.N. Dekhtiar), while other groups are represented as follows: Foramenifera (26), Radiolaria (1), Heliozoa (10), Labyrinthulida (1), Zoomastigina (about 40), Opalina (2), Apicomplexa (60), Microsporidia (160), and Myxosporidia (184). Some ecological groups of Protozoa remain poorly studied: apart from some publications by M.P. Bozhko, information on soil protists is almost completely absent.