Benzoin, which reacts specifically with arginine-containing peptides, was used as a pre-column fluorogenic reagent in the HPLC analysis of gonadotropin-releasing hormone (GnRH) and its synthetic analogues in an attempt to improve their detection sensitivity. The reaction kinetics of benzoin with GnRH and its structurally-related analogues, which all contain an arginine residue in the peptide chain, were investigated in this study. A fluorescence detector (ex 325 nm/em 435 nm) was used to detect benzoin-arginine derivatives. Another set of excitation and emission wavelengths (289 nm/344 nm), where fluorescent activity results from the aromatic amino acid residues, such as Tyrosine and Tryptophan, was used for comparison. The derivatization reaction and the fluorescent derivative product were highly affected by peptide concentration and heating time. The reactivity of arginine at position 8 was found to depend on the primary structure of GnRH and its analogues. However, it was observed that GnRH and its analogues were extremely unstable, as indicated by the labile nature of GnRH and its analogues under the derivatization conditions used.