Force field methodology (AMBER) has been used in conjunction with X-ray crystallographic data to evaluate the importance of attractive van der Waals forces in complexes of d(CGCGAATTCGCG)(2), d(CGCAAATTTGCG)(2), and d(CGCGTTAACGCG)(2) with a variety of ligands. Large negative energies were obtained (-128 to -246 kJ/mol) which, with exception of netropsin, were insensitive to base-pair sequence.