Peptide GFSKAELAKARAAKRGGY folds in an α-helical conformation that is stabilized by formation of a hydrophobic staple motif and an N-terminal capping box (Munoz V, Blanco FJ, Serrano L, 1995, Struct Biol 2:380–385). To investigate backbone and side-chain internal motions within the helix and hydrophobic staple, residues F2, A5, L7, A8, and A10 were selectively 13C- and 15N-enriched and NMR relaxation experiments were performed in water and in water/trifluoroethanol (TFE) solution at four Larmor frequencies (62.5, 125, 150, and 200 MHz for 13C). Relaxation data were analyzed using the model free approach and an anisotropic diffusion model. In water, angular variances of motional vectors range from 10 to 20° and backbone φ,ψ bond rotations for helix residues A5, L7, A8, and A10 are correlated indicating the presence of Cα-H, Cα-Cβ, and N-H rocking-type motions along the helix dipole axis. L7 side-chain CβH2 and CγH motions are also correlated and as motionally restricted as backbone CαH, suggesting considerable steric hindrance with neighboring groups. In TFE which stabilizes the fold, internal motional amplitudes are attenuated and rotational correlations are increased. For the side chain of hydrophobic staple residue F2, wobbling-in-a-cone type motions dominate in water, whereas in TFE, the Cβ-Cγ bond and phenyl ring fluctuate more simply about the Cα-Cβ bond. These data support the Daragan–Mayo model of correlated bond rotations (Daragan VA, Mayo KH, 1996, J Phys Chem 100:8378–8388) and contribute to a general understanding of internal motions in peptides and proteins.