Ninhydrin　was　found　to　exhibit　chemiluminescence　(CL)　when　it　was　oxidized　with　hydrogen　peroxide　in　neutral　or　weakly　acidic　solution.　Copper(II)　and　Co-II　can　catalyse　the　CL　reaction,　on　the　basis　of　which　ppb　levels　of　Cu-II　and　Co-II　can　be　determined.　In　the　presence　of　Cu-II,　some　amino　acids　enhanced　the　CL　reaction,　whereas　others　inhibited　the　CL　reaction　in　the　presence　of　Co-II.　A　flow-injection　system　with　CL　detection　was　developed　for　the　determination　of　some　amino　acids.　The　mechanism　of　the　CL　reaction　is　discussed.