Melatonin　and　some　of　its　important　derivatives　were　found　to　be　able　to　enhance　the　ECL　of　Ru(bpy)(3)(2+)　in　an　alkaline　Britton-Robinson　buffer　solution.　The　Optimum　conditions　for　the　enhanced　ECL,　such　as　the　selection　of　applied　potential　mode,　type　of　buffer　solution,　pH　effect　and　effect　of　Ru(bpy)(3)(2+)　concentration　have　been　investigated　in　detail　in　this　paper.　Under　the　optimum　conditions,　the　enhanced　ECL　is　linear　with　the　concentration　of　melatonin　and　its　derivatives　over　the　wide　range,　and　the　detection　limit　for　these　compounds　was　found　to　be　in　the　ran-e　of　5.0　x　10(-8)　to　1.0　x　10(-10)　mol　L-1.　The　proposed　procedure　was　applied　for　the　determination　of　drug　tablets　with　recoveries　of　85-93%.　A　possible　mechanism　for　the　enhanced　ECL　of　Ru(bpy)(3)(2+)　by　melatonin　and　its　derivatives　was　proposed.　and　the　relationship　between　molecular　structure　of　melatonin　and　its　derivatives　and　the　enhanced　ECL　behavior　was　also　discussed.　(c)　2004　Elsevier　B.V.　All　rights　reserved.