Nuclear magnetic resonance spectroscopy (NMR) is a powerful technique for determining the structures, dynamics and interactions of molecules, and the derived information can be useful in drug design applications. This article gives a brief overview of the role of NMR in drug design and illustrates this role with examples studied in our laboratory in recent years on disulfide-rich peptides, including cyclotides and conotoxins. Cyclotides are head-to-tail cyclized proteins from plants that are exceptionally stable and hence make useful templates for the stabilization of bioactive peptide epitopes as well as potential leads for anti-HIV drugs. Natural cyclotides target cell membranes, so understanding cyclotide-membrane interactions is useful in applying cyclotides in drug design applications. NMR studies of these interactions are described in this article. Conotoxins are disulfide-rich peptides, from the venoms of marine cone snails, which are of pharmaceutical interest because they potently interact with a range of ion channels, transporters and other receptor sites implicated in disease states. Chemically re-engineering conotoxins to give them a cyclic backbone has been used to engender them with improved biopharmaceutical properties, such as are observed in cyclotides.