Alkaline Phosphatase (ALP) belongs to the Hydrolase class of enzymes and catalyses the splitting of organic phosphate esters, with optimum activity at pH 10.20 is ubiquitously distributed throughout the body. However, liver, bone and placenta contain very high concentrations of ALP. Hence, increase in ALP activity is usually related to hepatobiliary and bone disorders. Elevated ALP levels are seen in toxic hepatitis, infective hepatitis, intra and extra hepatic obstructions. High ALP levels are also seen in osteomalacia, rickets and bone Cancer. The use of p-Nitrophenyl Phosphate (p-NPP) as a substrate for ALP assay produces a chromogenic product, p-Nitrophenol (PNP) which is quantified directly.