Recent advances in multidimensional nuclear magnetic resonance methodology to obtain 1H, 15N and 13C resonance assignments, interproton distance and torsion angle restraints, and restraints that characterize long-range order, coupled with new methods of structure refinement and novel methods for reducing linewidths, have permitted three-dimensional solution structures of single chain proteins in excess of 250 residues and multimeric protein in excess of 40 kDa to be solved. These developments may permit the determination by nuclear magnetic resonance of macromolecular structures up to molecular weights in the 50-60 kDa range, thereby bringing into reach numerous systems of considerable biological interest, including a large variety of protein-protein and protein-nucleic acid complexes.