Details of the interactions of biological macromolecules (proteins and nucleic acids) in solution with each other and with small effector molecules, such as hormones and drugs, are being probed at the molecular level. Generally such interactions are mediated by conformational alterations in the macromolecule. The method of choice to investigate the conformations of proteins and nucleic acids in solution is nuclear magnetic reasonance (NMR) spectroscopy. We have used 1H, 2H, 13C and 31P NMR in combination with selective stable isotopic enrichment (2H and 13C) to study the conformations and solution properties of proteins and DNA. Currently we are focusing on the effects of base sequence on the conformational transitions of polydoxynucleotides and the effects of cytotoxic drugs on those transitions. We are applying 2-dimensional proton NMR to obtain relative atomic distances and hence are able to define DNA conformations and effects of drug complexation in solution in molecular detail.