The seasonal development of testate amoebae and ciliates was studied in two peatbogs with different pH values. The values of numbers of testate amoebae were seasonally changeable. The highest numbers of testate amoebae were found in spring and summer with the dominance of Areclla vulgaris, Nebela barbata and Cucurbitella sp. The density during the autumn was the lowest. The highest numbers of ciliate communities were noted in spring and autumn during the mass development of small Scuticociliatida and Colpodea. The density throughout the summer was the lowest. Generally, in the present studies the abundance of testate amoebae was correlated with the abundance of bacteria and heterotrophic flagellates. The density of bacterivorous Colpodea, Scuticociliatida and Cyrtophorida correlated positively with the density and biomass of bacteria. In low pH peatbog relations between microbial loop components were stronger.