The head-to-head dimer of the calicheamicin oligosaccharide domain exhibits an impressive nanomolar affinity for its specific DNA recognition sites and a substantially higher degree of sequence selectivity relative to the oligosaccharide monomer. In an effort to detennine the structural basis for these binding properties, the solution structure of the 1:1 complex between the head-to-head dimer and the self-complementary oligonucleotide d(CGTAGGATATCCTACG)(2) has been solved using H-1 NMR-derived distance and torsion angle constraints and molecular dynamics calculations. Complete sequence specific proton assignments of both the DNA duplex and the carbohydrate have been obtained by 2D-NMR. A total of 607 experimentally derived constraints were identified including 452 proton-proton distance constraints derived from NOESY cross peaks intensities and assigned hydrogen bonds, along with 155 dihedral angle constraints obtained from a detailed analysis of the multiplet structure of cross-peaks for the sugar rings and from qualitative analysis of nuclear Overhauser effects for the DNA backbone.