During the last century, scientists commonly underwent a procedure of preserving osteological material via chemical conservation. It was a standard routine, which continues to this day, especially when very rare finds, which are deposited in museums, are concerned. However, scientists assumed th at chemical conservation, which is supposed to protect the human remains from degradation, would actually prevent the aDNA from extraction and further analysis. Especially nowadays, when molecular methods are available and widely used in this research field. As a result of this procedure, many human remains are untouched by genetic analysis. This study focuses on the samples treated by chemical conservation, namely dental calculus of individuals from two burial sites dated back to the Great Moravian Empire (9th – 10th century AD). The first site Pohansko – Kostel, was excavated in the 1960s. The human remains have been treated by celluloid dissolved in amyl acetate and acetate solution. 409 graves were excavated, from which the individuals were selected based on the size and location of their dental calculus for purposes of our research. The other site is located in Znojmo – Hradiště. The excavation is recent and ongoing since 2007. These remains were never chemically treated, thus serving as a comparison for the isolation protocol and further analysis. The samples were selected based on the same parameters as those, which were applied to the samples from Pohansko – Kostel. The aDNA of dental calculus was isolated from both graveyards with MinEluteTM PCR purification Kit (Qiagen). The results were analysed thoroughly in order to clarify whether the conservation treatment enables further scientific research of such samples.