To　calculate　superoxide　dismutase　(SOD)　activity　rapidly　and　accurately　by　indirect　SOD　assays,　a　formula　based　on　the　ratio　of　the　catalytic　speed　of　SOD　to　the　reaction　speed　of　the　indicator　with　superoxide　anion　was　deduced.　The　accuracy　of　this　formula　was　compared　with　the　conventional　formula　based　on　inhibition　in　five　indirect　SOD　assays.　The　new　formula　was　validated　in　nearly　the　entire　SOD　activity　range,　whereas　the　conventional　formula　was　validated　only　during　inhibition　of　40-60%.　This　formula　might　also　be　used　for　the　assays　of　other　enzymes.　(C)　2016　Elsevier　Inc.　All　rights　reserved.