The overall aim of the project is to answer arising questions about putatively symbiotic entodiniomorph ciliates of the genus Troglodytella, their metabolism, role in great apes’ digestion and to describe possible co-evolution with their hosts. These protozoans still represent a neglected component of the parasitofauna of great apes and detail studies are urgently needed to estimate their significance of under natural and captive conditions. The ecosystem of colon of apes is similar to that of humans, and parallels between human and great apes’ digestion were studied to address the origin of several human diseases. Ignoring the presence of symbiotic ciliates in apes might significanlty distort results of such studies. Having no idea about the function of Troglodytella spp., we can only hardly discuss the similarities and differences of human and great apes´ digestive processes. Methods of standardized determination of various metabolic activities, developed for rumen protozoans, will be applied to Troglodytella abrassarti from chimpanzee, after its stabilization in in vitro culture. Method of cryo-preserving and archiving the isolates will be applied as a part of Genome Resource Bank strategy. The molecular phylogeny of Troglodytella isolates will be reconstructed using sequences of selected genes and the processes of the co-evolution of Troglodytella and great apes will be evaluated to provide a background for studies of the evolution of hominids´ digestion.