The present invention relates to a crystal structure of G-quadruplexes and its use. The invention provides a crystal of an intramolecular G-quadruplex structure having a hexagonal space group P6, and unit cell dimensions a=b=56.7 and c=42.1; .alpha.=.beta.=90.degree., .gamma.=120.degree. and a crystal of G-quadruplex having the three dimensional atomic coordinates of Table 1 or Table 2. These structures may be used in a computer-based method for the analysis of the interaction of a molecular structure with a G-quadruplex.