The thermal dependence of the C-13 reonances of individual residues in the model peptide, acetylW(EAAAR)3-Aamide, was analyzed in terms of a two-state transition. The correlation of the effects of temperature, pH, and salt concentration on C-13 NMR and circular dichroic measurements of this peptide suggest that both measurements observe a common two-state helix/coil transition. The thermodynamic parameters which characterize the thermal transition of each residue suggest that the helical conformation of the peptide is stabilized by hydrogen bonds and by burial of apolar surfaces and that the helical conformation melts as a largely cooperative unit. The terminal regions of the helix appear less frayed than expected from the Lifson-Roig statistical mechanical model for a peptide helix/coil transition, indicating contributions from stabilizing noncovalent interactions in addition to backbone hydrogen bonds.