AbstractThe role of the benthic ciliofauna of the Tsibulnik bay of the Kremenchug reservoir in the comsumption of the primary production of phytomicrobenthos and the destruction of organic Substances is shown. In July all over the buy ciliates had consumed 41 % of the benthic primary production. During the process, consumption rates had reached 1.34 kJ/m2d on seperate sections of the bottom. Sufficiently high is the role of these protists in the destruction of organic substances. They had destroyed 1.4… 1.5% of the whole mineralised organic substances in summer and 10… 11% in autumn. The authors made a conclusion on the importance of the benthic ciliofauna in the transformation of organic substances in an eutrophic