The　electrochemical　behavior　of　tryptophan　(Trp)　and　its　derivatives,　such　as　indole-3-acetic　acid　(IAA),　5-hydroxytryptamine　(5-HT),　5-hydroxy-indole-3-acetic　acid　(5-HIAA)　and　glycyl-tryptophan　(Gly-Trp)　peptide　at　a　glassy　carbon　electrode　modified　with　hemin　(hemin/GC　electrode)　by　electropoIymerization　have　been　investigated　in　detail.　The　results　showed　that　the　hemin/GC　electrode　would　catalyze　the　electrochemical　oxidation　of　Trp　and　its　derivatives,　based　on　which　a　differential　pulse　voltammetric　procedure　has　been　proposed　for　determination　of　Trp　and　its　derivatives.　Meanwhile,　the　electrochemical　reaction　mechanism　for　these　compounds　at　hemin/GC　electrode　has　been　also　investigated,　and　the　results　indicated　that　a　two　electron　and　two　proton　transfer　was　involved　in　the　electrode　reaction　process.　(C)　2002　Elsevier　Science　B.V.　All　rights　reserved.