Large number of guanine tracts in oncogene mdm2, which are responsible for development of tumor fenotype in liposarcomas, suggest formation of different G-quadruplexes is possible. The major aim of this diploma thesis was to determine the possibility of a G-quadruplex formation within inducibile promoter mdm2 and to determine the conditions where single structure would be formed. In addition to nucleotide sequence mdm2-15 (contains five guanin repetitions), we also studied two shorter sequences mdm2-14 and mdm2-25, which are shortend for the first guanine repetition from 3'- or 5'-end. With 1D 1H NMR experiments we defined the number of different G-quartets in G-quadruplexes and in combination with CD spectroscopy aimed at description of topological determinants (parallel, antiparallel and (3+1) topology). Two different cations, K+ in Na+, were tested for their ability to stabilize G-quadruplex structures and the former was recognized as more successful at stabilization of G-quadruplexes of mdm2. Among acidic, basic and neutral pH, the latter was found to be most suited for promoting formation of predominant species.