Alkaline phosphatase (ALP) catalyzes the hydrolysis of phosphate esters in alkaline buffer and produces an organic radical and inorganic phosphate. Changes in alkaline phosphatase level and activity are associated with various disease states in the liver and bone. Alkaline Phosphatase Assay Kit is a highly sensitive, simple, direct and HTS-ready colorimetric assay designed to measure ALP activity in serum and biological samples. It contains 10 substrate tablets providing convenience for multiple usages. The kit uses p-nitrophenyl phosphate (pNPP) as a phosphatase substrate which turns yellow (λmax= 405 nm) when dephosphorylated by ALP. The Kit can detect 10-250 μU ALP in samples.