We report here C-13(alpha) chemical shielding parameters for central Gly residues in tripeptides adopting alpha-helix, beta-strand, polyglycine II, and fully extended 2degrees structures. To assess experimental uncertainties in the shielding parameters and the effects of N-14-C-13(alpha) or N-15-C-13(alpha) dipolar coupling, stationary and magic angle spinning (MAS) spectra with and without N-15 decoupling were obtained from natural abundance and double-labeled samples containing [2-C-13, N-15]Gly. We find that accurate (<1 ppm uncertainty) shielding parameters are measured with good sensitivity and resolution in N-15 decoupled 1D or 2D MAS spectra of double-labeled samples. Compared to variations of isotropic shifts with peptide angles, those of C-13(alpha) shielding anisotropy and asymmetry are greater. Trends relating shielding parameters to the 2 structure are apparent, and the correlation of the experimental values with unscaled ab initio shielding calculations has an rms error of 3 ppm. Using the experimental data and the ab initio shielding values, the empirical trends relating the 2degrees structure to shielding are extended to the larger range of torsion angles found in proteins.