The DNA bound on the surface of the histone octamer in the nucleosome core particle partially protects the epsilon-amino side-chains of a subset of the lysine residues from reductive methylation. Most of the strongly protected lysines, which probably define the path of the DNA on the octamer surface, are in the globular ('structured') regions of the core histones rather than in the N-terminal or C-terminal 'tails'. Analysis of the protected peptides shows that the three strongest lysine-containing DNA-binding sites in the core histones contain the sequence-Lys/Arg-Lys-Thr/Ser-. On the assumption that the lysine-containing regions protected from chemical modification are also those found in lysine-DNA cross-links in another study [Mirzabekov et al. (1978) Proc. Natl Acad. Sci. USA 75, 4184-4188], particular DNA-protected peptides may be tentatively assigned to particular DNA contact points. This leads to a more detailed description of the DNA-binding regions on the octamer surface in the nucleosome core particle. Strong contacts, reflected in strongly protected lysines, may well contribute to the distortion of the DNA from smooth bending [Richmond et al. (1984) Nature (Lond.) 311, 532-537].