Two different, theoretical studies of intramolecular proton-proton distances in polypeptide chains are described. Firstly, the distances between amide, C α and C β protons of neighbouring residues in the amino acid sequence, which correspond to the sterically allowed values for the dihedral angles φ i, ψ i and χ i 1, were computed. Secondly, the frequency with which short distances occur between amide, C α and C β protons of neighbouring and distant residues in the amino acid sequence were statistically evaluated in a representative sample of globular protein crystal structures. Both approaches imply that semi-quantitative measurements of short, non-bonding proton-proton distances, e.g. by nuclear Overhauser experiments, should present a reliable and generally applicable method for sequential, individual resonance assignments in protein 1H nuclear magnetic resonance spectra. Similar calculations imply that corresponding distance measurements can be used for resonance assignments in the side-chains of the aromatic amino acid residues, asparagine and glutamine, where the complete spin systems cannot usually be identified from through-bond spin-spin coupling connectivities.