To　investigate　the　reactive　oxygen　species　(ROS)　distribution　in　living　animal　tissues,　two　ROS　indicators,　dichlorofluorescin　diacetate　(DCFH-DA)　and　MitoSOX™　Red　were　applied　to　visualize　ROS　on　the　frontal　interior　abdominal　wall　of　living　SD-rats　by　tail　vein　injection　and　local　smearing　respectively.　Revealed　was　an　unexpected　ROS　distribution　pattern.　ROS　were　demonstrated　in　a　few　vertical　fluorescent　lines,　which　related　to　neither　veins　nor　nerves　but　could　be　almost　perfectly　superimposable　on　a　standard　human　acupuncture　meridian　network.　The　phenomenon　that　cells　with　high　ROS　content　should　be　aligned　in　a　regular　manner　is　interesting　as　well　as　its　resemblance　to　meridian　system.　©　2009　Elsevier　Ltd.　All　rights　reserved.