The　interaction　between　quinidine　sulfate　(QDS)　and　congo　red　(CR)　was　studied　using　resonance　light　scattering　(RLS)　technique,　ultraviolet-visual　spectrophotometry　and　fluorimetry.　In　weak　acidic　medium,　QDS　reacts　with　CR　to　form　a　supermolecular　complex　which　results　in　the　enhanced　RLS　intensity.　Some　important　interacting　parameters,　such　as　the　solution　acidity　and　CR　concentration,　salt　effect　and　addition　order　of　the　reagents,　were　investigated　and　optimized.　Under　the　optimum　conditions,　it　was　found　that　the　enhanced　RLS　intensity　was　in　proportion　to　the　concentration　of　QDS　in　the　range　0.2-8.4　mu　g　mL(-1).　The　corresponding　detection　limit　was　12.0　ng　mL(-1).　The　results　showed　that　this　new　method　enabled　simple,　sensitive　and　rapid　determination　of　QDS　and　was　used　for　the　determination　of　QDS　in　urine　and　simulated　huamn　serum　samples.　Copyright　(C)　2009　John　Wiley　&　Sons,　Ltd.