AbstractAqueous solutions of three tryptophan‐rich growth hormone releasing hexapeptides, GHRP‐6 (His‐D‐Trp‐Ala‐Trp‐D‐Phe‐Lys‐NH2), hexarelin (His‐D‐2‐Me‐Trp‐Ala‐Trp‐D‐Phe‐Lys‐NH2), and EP7458 (His‐D‐Trp‐Ala‐2‐Me‐Trp‐D‐Phe‐Lys‐NH2), were exposed to varying durations of ultraviolet (UV) light. Using NMR spectroscopy, first‐order rate constants for the UV photolytic degradation of the tryptophan(s)/2‐methyl tryptophan residues within each peptide were obtained by plotting the decrease in the area of the indole N‐H resonances with respect to UV photolysis time. A significant differential photolytic effect was observed between the two tryptophan residues of GHRP‐6 and the tryptophan/2‐methyl tryptophan residues of EP7458. A somewhat smaller differential photolytic effect was observed between the tryptophan/2‐methyl tryptophan residues of hexarelin. In addition, the three peptides were degraded at different rates, suggesting that the effect of UV light on each peptide is dependent on whether a tryptophan or 2‐methyl tryptophan is the second or fourth residue in the pri