We show that protein structures in solution can be refined by using C-13(alpha) and C-13(beta) chemical shifts. We investigated 12 alanine and 8 valine residues in the nuclease from Staphylococcus aureus and found that the phi, psi, and (chi) values of these residues are closer to the X-ray phi, psi, and (chi) values when nuclear Overhauser effect distance restraints and J-coupling torsion angle restraints are supplemented with chemical shift restraints. For phi in particular, the rmsd versus the X-ray structure is similar to 10 degrees with chemical shift restraints versus similar to 20 degrees without chemical shift restraints. Both "fully-restrained" families of structures, those determined with and without chemical, shift constraints, had small numbers of minor NOE violations. However, the chemical shift restrained structures were consistent with experimental Ala and Val C-13(alpha) and C-13(beta) chemical shifts, whereas the structures determined without shift restraints yielded back calculated chemical shifts in poor accord with experiment. Carbon-13 chemical shifts therefore appear to be of use in protein structure refinement when used in conjunction with chemical shift surfaces computed using ab initio methods.