Forty resonances in the proton magnetic resonance (p.m.r.) spectrum of hen egg-white lysozyme have now been assigned to specific amino acid residues by using methods outlined in the preceding paper (Campbell, Dobson & Williams 1975 $\alpha $). The analysis of both the broadening and shift perturbations of these resonances by lanthanide cations bound at a single site provides definite evidence that there is a close similarity between the p.m.r. solution and X-ray crystal structures. More detailed quantitative structural correspondence cannot be established readily for the p.m.r. study has demonstrated that certain sidechain groups are mobile, and the solution structure is sensitive to the precise ionic size of the lanthanide cation. The assigned resonances have been used to detect and investigate local conformational changes in the active site of the protein brought about through binding of protons, metal ions and inhibitors. Kinetic as well as thermodynamic parameters can be extracted from the measurements.