Previous studies showed that microbial communities living in terrestrial or aquatic mosses have a good potentiality to be early indicators of the presence of contaminants (or of some nutrients) in ecosystems. Indeed, the comparison between abundance and biomass of different microbial groups such as primary producers / predators / decomposers can give valuable information about the nature of a disturbance. These studies also showed that some microbial groups, and particularly the unicellular eukaryotic predators, seem to respond significantly to many kinds of contaminants, probably because they are affected both directly (through toxic effect) and indirectly (e.g. through trophic interactions) by the disturbance. Testate amoebae stand out among the different groups of potential microorganism bioindicators. Indeed, the presence of a shell constitutes an important advantage for future applications. It allows to collect and to preserve samples without fixative, and to store them easily. Furthermore identification of morpho-species by trained technicians is possible. Testate amoebae may therefore be used as atmospheric or water contamination indicators in the near future. However, more studies are needed in different ecosystems and under different contaminations and ultimately to standardize their use and define a “testate amoeba bioindication index”.