High levels of alkaline phosphatase activity are characteristic of bone disease with increased osteoblastic activity, hepatobiliary disease with partial or complete biliary obstruction and transient hyperphosphatasemia in children. A gamma-glutamyl transpeptidase is often useful to differentiate whether an elevated alkaline phosphatase originates in the bones or the liver. A normal gamma-glutamyl transpeptidase suggests bone origin. A serum alkaline phosphatase isozyme pattern by electrophoresis is also necessary to differentiate various pathological states.